Pretty much anything is possible if you're willing to put the work in. But if you can't find any existing romhacks, then that means no one has really tried before, which means there's that much more work to do.
There is an awful lot of enthusiasm for hacking Sonic games in general, but I don't think Sonic Spinball has ever been particularly popular, so it would not be surprising if it has gone largely untouched.
Also, there is no such thing as "a hacking program that supports any mega drive rom". Some ROMs might have common features, but usually particular details like level structure have to be worked out from scratch for every game.