OK, so i am working on a workaround to the fact that the Battle Difficulty Slider doesn't work.

The idea is pretty simple; since i cannot modify the battle difficulties themselves(TExc_ImplementedTables notes that table battle_difficulty_modifiers is implemented but non-pack and so not open to modifying) i will workaround to transcribe every campaign effect/bonus/etc that applies to the campaign difficulty you want into every campaign difficulty. This way when you start the game you will choose the battle difficulty you want to play with, and then install a mod to set the effect of the campaign difficulty to the desired campaign difficulty for every difficulty.

Where I am at:

More or less i have been able to identify the relevant campaign difficulty effects in the following tables. cai_variables, campaign_variables, cai_personality_empire_rivalry_components,effect_bundles_to_effects_junctions, cdir_events_mission_option_junctions, and effect_bundles.

campaign_variables appears to modify global campaign effects that occur on the global window. Bonus starting cash, and number of units required to prevent retreats and such.

cai_variables appears to modify simply AI behavior based on varying effects in the game world.

cai_personality_empire_rivalry_components appears to modify a multiplier to expansionist disapproval for diplomacy.

effect_bundles_to_effects_junctions appears to modify the upkeep cost for additional armies and effect_bundles appears to modify the description of the upkeep cost effect.

cdir_events_mission_option_junctions appears to modify the duration before missions time out.

campaigns_campaign_variables_junctions modifies the speed and initial size of rebel creation. It appears to be missing values for normal difficulty which may be an issue similar to cai_variables_overrides but its unlikely that this will have a large effect as most the the variables are close together anyway.

campaign_difficulty_handicap_effects appears to modify campaign effects by difficulty... however it may be applied to AI's/factions individually from cai from cai_personality_group_overrides and not simply a global effect. Disambiguating this may be difficult. It may also be unnecessary.

The above appear to be pretty simple "copying the intended difficulty modifier to every difficulty" fixes.

What i really need help with

Slightly more complicated is cai_variables_overrides. This appears to override ai behavior based on difficulty level. Unfortunately it does not contain entries for every difficulty level and effect and isn't set up in a way to make it clear that these can be changed. If i insert new keys in the database in order to force the "normal" effect to the "hard" effect can this break the scripting in the game? Will it take? This occurs in some of the tables above, but in a manner that is clearly non-intrusive (I.E. replace the effects with 0 on the assumption that a non-listed effect is zero. But its not necessarily simple to move a non-listed effect to a value). This is specific to they key "CAI_VARIABLE_MAX_CONFEDERATION_STRENGTH"

Additionally there are three other tables which modify AI personalities. cai_personalities, cai_personality_group_overrides, start_pos_factions.

I am not really sure at all how these interact or set AI personalities. And, more over, i don't really see a way to guess and check in game. It appears that cai_personalities defines how personalities should act. The problem is that I am unsure that each faction has a 100% set personality based on difficulty. If they do, then i can simply edit cai_personalities to have all the same behaviors based on the deterministic chosen personality... but it appears that many of these should be random in some way.

Similarly cai_personality_group_overrides seems to set AI personality based on difficulty... or it sets difficulty bonuses based on AI personality. If they go one way then editing it as if it went the other will break things super hard. If it goes the other way then modifying this would actually make modifying the entire difficulty structure very easy. Either way this seems like a key to getting things right.

start_pos_factions also appears to contain ai information. I am not sure how this interacts with the above two tables to produce the personalities and difficulties associated with them.

I am also not particularly happy about having to modify the above three tables, since it seems like the information is dependent on owning/not owning the DLC. (in that AI values may or may not be specific to the faction you choose, and since i do not have much of the DLC i may not be able to modify those if they're kept in a different data folder). So if i can get the right AI behavior without doing that that would be ideal.

I am also not proficient in SQL(or database organization in general) so there may be some database organizational structure that i have missed that would answer these questions.

Also worth noting that i have roughly complied these tables by searching for difficulties themselves "hard/very hard", searching by "difficulty", and manually perusing the *_variables,*_difficulty, and cai_* tables. However campaigns_campaign_variables_junctions contains a field by the name of "optional_difficulty_level" and the search feature does not appear to allow me to