There are certain technical assumptions made, when I was making it for M4 K4.

Its reducing M4 JCMs when the morph is dialed, for example, so they do not distort the smaller figure. These are recognized by name (JCMxxxx, JSMxxxx). I didnt check if this the same for DAZ3, for example. But looking at David, he seems to follow the same pattern.

So yes, its working directly on the geometry, mainly.

Whats M4/V4 hard-coded is the bulge intensity tweak script. This is looking for specific obj files to detect figure type. So this wont work with DAZ3, but if DAZ3 bulge intensity is in general not very different between the figures, then this wouldnt matter so much. One has to try and see. The M4 vs K4 bulge settings are similar, with V4, there is more difference.

And yes, what you write about custom characters, I'm thinking about this too.