From looking into it, if I understand it correctly, a "module" is a set of different purchasable costumes in-game. It seems right now we're lumping all of these different costumes for several different characters into a single gentag.
I suppose it's one of those cases where we started doing it this way 15 years ago and nobody objected so here we are.
As an example: swimwear_(module) megurine_luka actually contains post #4074633 (swimwear), post #2407289 (swimwear P), post #1256618 (resort bikini) and a bunch of other random skins. It appears all of these skins have their own name, judging from the fandom wiki.
So yes, if someone wants to put in the work they can create individual tags for these costumes. So basically it would mean moving the posts from swimwear (module) to, for example, megurine_luka_(swimwear_p) or megurine luka (racing swimsuit) or hatsune miku (swimwear s).
The fandom is a good place to start, since they have all the names and a gallery linking to individual pages for each costume. For example: https://project-diva.fandom.com/wiki/Hatsune_Miku:_Project_DIVA_Arcade_Future_Tone/Modules
You're free to do this if you want. All the module tags are fairly small, so it would make sense to tackle and empty them one at a time.
You can get a more complete list of tags from the tags search, since the wiki is most likely out of date.