This tutorial is originaly by Gundug. With his permission, I am posting this for others since I have received several pm's on this. All credit goes to Gundug.
First of all, the easiest part is to edit descr_sm_factions.txt. Do a search for Saxons(Or the faction you're wanting to change). In their block of code, under religion, change catholic to pagan. Their priests will now convert regions to the Pagan religion.
Next open export_descr_buildings.txt. Do a search for "church" and this should bring you down to the code for Catholic churches. You can copy this entire block, from the start that begins "building temple_catholic" to the end "}" symbol that appears just before "building temple_orthodox". This is a very large block of code, and includes every Catholic church available for both cities and castles.
Once copied, the easiest way would probably be to paste the block at the end of the file, just below the existing "building temple_pagan" that is used by the Aztecs. The Saxons will not use that building though, only the new ones we are creating. At the beginning of the block you just copied, change "temple_catholic" to something new (in my case, I am calling it "temple_s_pagan"). Right below, where it says convert_to "temple_catholic_castle", change the name (in my case, I used "temple_s_pagan_castle"). On the next line, change religion to pagan.
Under levels, change the names of each upgrade (since I am lazy, I just added _p to every building, so: levels small_church_p church_p abbey_p cathedral_p huge_cathedral_p).
Below this, where it shows small_church city requires factions { normans, de..., change small_church to small_church_p and get rid of all of the factions shown within the { }. Add saxons in place of them. The result should be something like this: small_church_p city requires factions { saxons, } (be sure to keep all the spaces, commas, etc. that the original lines of code use)
In the block under "capability", get rid of all the priest recruitment options you will not need and leave only an option for the Saxons. Ex: agent priest 0 requires factions { saxons, }
Below, under "upgrades" change "church" to the name you used for the next level of building - in my case: "church_p".
Here is my finished building block for small_church_p:
small_church_p city requires factions { saxons, }
{
convert_to 0
capability
{
agent priest 0 requires factions { saxons, }
happiness_bonus bonus 1
religion_level bonus 1
pope_disapproval 1
agent_limit priest 1
}
material wooden
construction 1
cost 800
settlement_min town
upgrades
{
church_p
}
}
You must simply follow the same pattern for the next buildings in the list. The castle temples work in the same way as the city versions. Just be sure to change the "convert_to temple_catholic" to the name you used for the city category - in my case: "temple_s_pagan".
Once all of the buildings have been modified, you can then edit export_descr_buildings_enums.txt. Do a search for "small_church". Copy the entire block of names from that to "chapel_southern_european_desc_short" and paste them either to the end of the file, or to keep all of the churches together, you can paste the new block after one of the other groupings. You will then need to rename every line so the building reflects what you entered in the buildings file.
Example:
small_church_p
small_church_p_desc
small_church_p_desc_short
small_church_p_northern_european
small_church_p_northern_european_desc
small_church_p_northern_european_desc_short
small_church_p_mesoamerican_desc
small_church_p_mesoamerican_desc_short
small_church_p_middle_eastern_desc
small_church_p_middle_eastern_desc_short
small_church_p_eastern_european
small_church_p_eastern_european_desc
small_church_p_eastern_european_desc_short
small_church_p_greek_desc
small_church_p_greek_desc_short
small_church_p_southern_european
small_church_p_southern_european_desc
small_church_p_southern_european_desc_short
Once that is done, search for "temple_catholic_name" in the same file. Copy that and "temple_catholic_castle_name" and paste the block of text where you would like them to appear. Right below is probably easiest. Change those to what you used for the category of the churches. In my case it would look like:
temple_s_pagan_name
temple_s_pagan_castle_name
After all of this is done, I think you should be done with all of the basic building creation work. Now you need to define the names for the buildings. To do this, go to the "text" folder. Hopefully, there are regular txt files that you can edit there. If not, you will need Alpaca's strings_bin converter, which you can get here: http://forums.totalwar.org/vb/showthread.php?t=75229
Once you have workable txt files, you will need to edit export_buildings.txt. Open that file and do a search for small_church. Copy from the dividing line between records (looks sort of like this: ¬--------------) all the way down to where it says:
{chapel_southern_european_desc_short}
A Chapel converts a small percentage of the region to Catholicism, improves happiness, and allows the Priest agent. You can paste the huge block down at the bottom of the file.
You then need to rename every listing for the churches to match what you called them in export_descr_buildings.txt.
Below is an example of a listing for one building.
For my listings, I just needed to copy and paste a "_p" after church, since that is how I named the buildings. Be sure to change every one of the names in { } to match the new names you used, including the versions for other cultures. (note: you will not need to change every text description (shown in dark red) that follows the name in brackets if you don't want to, just the northern_european ones, since Saxons are northern_european, and no faction from another culture will need these churches - unless you change that).
{small_church_p} small_church_p
{small_church_p_desc} DO NOT TRANSLATE
{small_church_p_desc_short} DO NOT TRANSLATE
{small_church_p_northern_european} Small Church <--change this to whatever you would like to call the first level temple
{small_church_p_northern_european_desc}
With devotion to God prevalent in medieval times, even the smallest of churches are an important building in the communities they grace. Though relatively humble by Catholic standards, small churches are still well built, and are typically one of the most impressive buildings in their locale. <--change this description to whatever you like
{small_church_p_northern_european_desc_short}
A Small Church converts a very small percentage of the region to Catholicism, and improves happiness. <--change this as well
{small_church_p_mesoamerican} Small Church (this and all the following text descriptions can either be copied directly from the northern_european ones, or you can leave them alone. These other factions will never be able to build these churches, so it will not matter)
{small_church_p_mesoamerican_desc}
With devotion to God prevalent in medieval times, even the smallest of churches are an important building in the communities they grace. Though relatively humble by Catholic standards, small churches are still well built, and are typically one of the most impressive buildings in their locale.
{small_church_p_mesoamerican_desc_short}
A Small Church converts a very small percentage of the region to Catholicism, and improves happiness.
{small_church_p_middle_eastern} Small Church
{small_church_p_middle_eastern_desc}
With devotion to God prevalent in medieval times, even the smallest of churches are an important building in the communities they grace. Though relatively humble by Catholic standards, small churches are still well built, and are typically one of the most impressive buildings in their locale.
{small_church_p_middle_eastern_desc_short}
A Small Church converts a very small percentage of the region to Catholicism, and improves happiness.
{small_church_p_eastern_european} Small Church
{small_church_p_eastern_european_desc}
With devotion to God prevalent in medieval times, even the smallest of churches are an important building in the communities they grace. Though relatively humble by Catholic standards, small churches are still well built, and are typically one of the most impressive buildings in their locale.
{small_church_p_eastern_european_desc_short}
A Small Church converts a very small percentage of the region to Catholicism, and improves happiness.
{small_church_greek} Small Church
{small_church_greek_desc}
With devotion to God prevalent in medieval times, even the smallest of churches are an important building in the communities they grace. Though relatively humble by Catholic standards, small churches are still well built, and are typically one of the most impressive buildings in their locale.
{small_church_p_greek_desc_short}
A Small Church converts a very small percentage of the region to Catholicism, and improves happiness.
{small_church_southern_european} Small Church
{small_church_southern_european_desc}
With devotion to God prevalent in medieval times, even the smallest of churches are an important building in the communities they grace. Though relatively humble by Catholic standards, small churches are still well built, and are typically one of the most impressive buildings in their locale.
{small_church_p_southern_european_desc_short}
A Small Church converts a very small percentage of the region to Catholicism, and improves happiness.
Once you have changed the descriptions for every level of church you created (a ton of work), you should be almost done. Now do a search for {temple_catholic_name}. Copy that and the {temple_catholic_castle_name} blocks and paste, just below, if you like. Edit those to reflect the correct names - in my case:
{temple_s_pagan_name}
Churches <-- whatever you want to call these buildings
{temple_s_pagan_castle_name}
Churches
After that, save, and you should be all set. There will not be good images in the game to represent the new buildings (the game will use a generic building image), but everything should be working.
As for the images for the buildings, I will add how I got it to work later. But the above is a start if you're wanting to make thoses changes.