I'm pretty sure 'local variables stored on a character' do NOT transfer over between modules. For a very good reason -- NO local variables are stored on a character! Anything 'set' on a character are set on an object in the game and stored with the savegame file. They're in no way persisted with the character.
Even in the official campaign, all cross-module info was 'carried' via items. The henchmen quests in later acts were in no way based on whether or not you were their 'friend' or had adventured with them enough, rather... did you have the 'item' that they gave in the earlier module. (Likewise Aarin Gend's amulet)
It seems the best you could do would be to give a character an amulet or a book where the tag or text associated with it carried the (limited set of) information you needed to send between modules. If you can modify the text of a book item programatically, for example, you could store several pieces of info there, and retrieve from another module.
If it's a limited amount of yes/no info, the presence of an item would suffice.
BTW, I'm moderately adverse to large mods to the game that involve any file changes (hak paks or otherwise). If a mod/hack was extremely well done I might try it though.