>>33375291>>33376424they have "some" input and can change minor designs, the base design will always stay the same. The models are chosen for them and they can make minor tweaks, that's pretty much the process.
Also, depending on the artists, there's some change that they can refuse to do if they don't like it. Gura wanted a ahoge added to her model, since it was a small change it was possible, but her artist refused and thought it would have made her character look worse than without it.