OnShape has the entire machine waiting for you to modify...
[
cad.onshape.com]
Not sure what CAD app you're most familiar with but I've been doing more and more with OnShape lately -I have an educator license of Inventor that I typically use... and I've dabbled with OpenScad as well, enough to know how to hack anyway.
The file mgmt. in Onshape is a bit wonky at the moment, I think you want to open the above link, and then "clone" the project to your folder(give it a custom name like DjDemonD - xxxx etc... and they you have a custom version to hack at there is also a way to copy/paste out individual parts. I know I was able to do this once -I started working on a custom mount for the E3D hotend + partfan.