hi, i tried to look at page 220 for the mod insertion, and i have some doubts: what if in the mod there are folders that are not mentioned in those lines? i don't know where they belong, or should i leave them be?
I can probably answer this one. The folder in question works a bit like the overrides folder in GTA5 if you've ever modded that. In FF7, there are a bunch of lgp files, which are basically zip files containing a bunch of files in a specifically named file. There are lgp files for battle, magic effects, character models, etc.
The Reunion injects replacements to those files either by replacing the lgp file outright or creating a folder with the same name and file contents as the lgp file. You can see this if you look at the structure of The_Reunion\BASE\New_Translation and The_Reunion\BASE\Model_Overhaul as both contain a collection of files. The ini file determines which folders of overrides gets loaded and in what order.
If you specify an empty folder name on the MOD_ID section of the INI file, then start the game, it will create the folder structure you need automatically. After that, if you wanted to use a model for example from 7th Heaven, you would use the IRO tool to extract out the download that has the model you like. The field mod, find the model you like and when you open it, you'll find a folder. It will be named either char or char.lgp. If you place that folder in the The_Reunion\CUSTOM\YourModFolder\direct, which also should now contain a char folder, any folders in that folder will override the ones injected by Reunion. All the compatible mods will have a matching folder structure.