Just wanted to let you guys know I've found all the engine names for all the abilities, talents, skills, and am making a complete video tutorial on creating custom henchmen, along with class presets, skin/hair/head previews. Should be posted sometime tonight, it's quite a slow process, but almost done.

You can add any skill, as far as I can tell, that's in the game files to your character so long as they meet any requirements. This includes consumables, so you can give a Ranger every arrow type (that is normally consumable), and it will be used as an unlimited skill. Rogues also have a Talent that must have been disabled or something, called Mark the Knife, that gives an AP bonus to daggers. You could also add Staff of Magus this way, but luckily they patched it so henchmen get it now. Oh and I think this also works for scrolls, because you can add Unlock Magic (lets you unlock magic locks) as a skill in your toolbar too.

Thanks to Norbyte and nates for helping guide me on all this, hopefully the guide will help a lot of people who just want custom dudes!