Tbh can't you just use a patcher maker to update all the altered files from the previous version of Tiara's files? That's what I distribute for other games o-o And the patcher's file is dependent on the amount of editing you make to the original file, and since each update would only add a few lines to things like .xml's, it shouldn't be too large.
Then you make installers for large updates like Generations updates.
Edit: Though, that'd mean either a lot of work for you, or everyone would have to do full installations of Tiara. (Or just make patchers for the files pretty much everyone uses (E.g. .txt files, .xml files)