Yeah, everytime I implement something like this it even amazes myself how rediculously easy things become.
Note though that this import is done the same way as models so that the size of BG.PAC will always increase, nothing is replaced or removed from the file. There should be a theoretical max both for characters and arenas since the file size could become so large that the offset can't be represented in the plistps2.arc.
How much this theoretical max is, I don't know. I haven't calculated it. If someone here knows how this is done and wants to display their math skills, please calculate it so that we know how large a CH or BG file can get. That way I know if I need to rethink the functionality so that it could rebuild/replace things in the files and not just add to them.