There's another program called Space Claim which apparently does similar after-development editing and accepts a miriad of file types. http://www.spaceclaim.com/en/default.aspx

I'd like to see these packages actually work on the sort of geometry we typically do before believing their claims. ;)

The simple truth is, when it comes to beautiful forms that can be built in MoI (or my workplace standard Solidworks) changes rarely involve the moving of a warts (this is the Industrial Designer Snob term for anything tacked onto the base form) but instead involve having to grow, shrink, stretch or otherwise readjust the initial beautiful form so that it fits the new requirements but remains both beautiful and tightly numerically controlled, and drafted etc etc. (Hence the reason that the tightly constrained Solidworks is not the best choice for the sort of free flowing surfaces MoI can handle with ease...)

I just have to look at MoI the way I do Artrage verses Illustrator. In the former you've got all the tools to accuracy too, but you just have to be willing to commit and live with it! (Fear of committment issues here.)

-Greg