At this point I don't know if there is a significant difference between editing one of the text files directly, or editing an xsml file and then having it generate a new text file.
Not much, the game only loads the .txt file, editing the .xlsm file is less eye straining tho
I also did a quick test to see if using partial Characters.txt files is possible in the game, and it seems that the engine loads them correctly.
Adding this to a new Characters.txt in a test mod:
new entry "NormalPlayer"
type "Character"
data "Vitality" "500"
... will add an extra 500% vitality to your characters in normal mode, overriding the original 0% and leaving everything else intact.
Some changes (skilldata.txt changes are among them) are applied retroactively to all savegames, you don't have to create a new game for them, as the savegame doesn't contain the properties of your skills, only the skill name references.
Yet if I modify it to consume 1 or 2 AP, it will cost 3! It appears that the minimum it can successfully be set to is 3, and I have no idea why.
TBH I don't think I've ever seen any action in the game that takes less than 3 AP.
Attacks are at least 3-4AP; using inventory items is 3AP; etc.
This skillset.text file also contains the descriptions for the spells. But if I edit the description, like setting Staff of Magus to say it is a 'super awesome laserbeam' instead of 'missile,' the change isn't reflected at all. Likewise editing the base attributes of the player character (so base strength would be 8 instead of 5, for example) has no effect whatsoever.
I think that texts cannot be changed in SkillData.txt directly; you also have to change the relevant string entry in Localization\English\english.xml:
<content contentuid="hfd7a96cdgb2dcg43adgbe2bg3023fab2f2e9">Launch a magical missile from your staff that deals [1] damage.</content>
... or Public\Main\Localization\Stats.lsb, which contains the same text and content UID.
