Is it problematic to change the common.tad? It's just to use the japanese fonts instead, if I copy them into their own tac/tad the mod is ~250MB bigger, which is not really a big deal but since the files are already there...
Good question. I'll try to answer it as simplistic as possible:
TAD/TAC are an archive container format presumably created by d3t. When the game boots, the game looks at the timestamp and filename etc of each TAD/TAC pair found in the archives folder. Whichever TAD/TAC is the latest, gets read in that order. For this reason, TAD/TACs are how d3t patched the game.
The main advantage behind creating your own TAD/TAC? Well, you're modifying game content the way d3t implemented this kinda thing. Meaning you can neatly put your mod files in your own TAD/TAC file, drop them into the standard "archives" folder and that's it. Mod installed.
So problematic? I'd say that your current version is pretty close to being a 'full native mod' and given that, I'd say "probably not so problematic" but then in the overall picture of things, I'd say it's problematic in the sense that if we wanted this mod on PS4, we might need to do some changes.. or...
I have a mod manager releasing very soon and native mods are a lot easier to manage than stuff which tries to change a few bytes in one of the TAD/TACs and would love to have your mod in it.
I love the work and effort etc, really good job. Of course, I could do it for you, or you could do it, whichever is best really.