As a partial effort to resolve some issues I have with vanilla SS6.4 (my original post here), I did a lot of forum searching to find out how to make the turn progression go back to 2 turns per year. I discovered that this has been requested before, but couldn't find anything that works with the submod manager (SS_Setup.exe).. so now that I think I've figured it out, here it is, SMM compatible 
Here's what this submod does:
- Works with Vanilla SS 6.4. I also use it with other submods - it shouldn't conflict with a submod unless the submod alters the time rate or includes an aging script.
- One turn is now half a year. Two turns per year (2 TPY). Generals and characters age 1 year after each *winter* turn is ended (half a year per turn), and time passes twice as slowly.
- Devastation is back in the game, and should be fixed (based on what people smarter than me have said on this forum). From what I understand, the aging script in SS 6.4 made devastation permanent, so devastation was removed... but since I removed the aging script devastation's no longer broken, so this adds it back.
* ( I tried to test devastation, but I gave up when no large rebel armies spawned. An army of 2 showed up with no devastation after a few turns - I hope that doesn't mean I failed at reintroducing devastation )
Possibly negative consequences:
- Historical dates and event triggers based on years will now take twice as long to occur. I assume this means that, for example, Mongols take twice as long to invade, new units take twice as long to be available in Real Recruitment, etc...
- I did not balance build times, training times, movement times, or anything like that. So basically you'll be accomplishing twice as much in the same amount of "in game time".
Note on other submods:
- Feel free to check out Meneth's Submod Compilation, which also comes with 2TPY. I didn't want all the other packaged stuff, plus he says it's incompatible with disabling Real Recruitment (which I always disable). He did post a 2TPY mod that worked in SS 6.3
- If you're quite new to Stainless Steel, I highly recommend getting the Weaker Heretics submod - maybe even the "even weaker" heretics mod
(heretics in SS 6.4 vanilla are way too strong)
Installation instructions:
- Just download the attached text file and put it in your C:\...\Medieval II Total War\mods\SS6.3\data\campaign\sub directory
- To implement it into your Stainless Steel installation, run your C:\...\Medieval II Total War\mods\SS6.3\SS_Setup.exe file
- Select Early or Late campaign, and make sure Two Turns Per Year is checked.
******Playing with this mod will require a NEW campaign******
And finally, a bunch of thanks:
I really can't take the credit for anything but putting what's already known into something manageable by SS_Setup.exe. The information is readily available on the forum and it will take far too long to credit everyone that had a hand in it. So instead of going by name, here's a list of forum posts I looked at to guide me along this process. I will note that tudor93 replied to my PM mere hours after I sent it to him - nice to have such a friendly community! Many thanks to those who contributed to the knowledge base in these posts: 