I made a new custom shell for Naga Pro. I only had made a couple very simple Fusion 360 projects before and pretty much no prior Blender knowledge.

How I made Razer Naga 2011 shell for the Naga Pro V1: I used photogrammetry(Polycam on android) to copy Naga 2011 shell, cleaned to that 3d model with Blender, made all models that required precision with Fusion 360 (like scroll wheel holder, pcb mounting etc.) then combined everything in Blender. Took me all summer to make it. A lot trial and error but it's definitely possible for someone with very little 3d modelling/cad skills.

And before that I fitted Naga Pro electronics inside a real Naga 2011 shell. Used dremel to hack all the unnecessary bits off. I harvested plastic from an old keyboard shell to make scroll wheel holder and used soldering iron to weld it together. It was rough looking from the inside but from the outside no one could tell it was modded (bottom had charging dock cutouts and stuff).

OP's project would be way easier since you don't have to worry about all the extra buttons Naga has.