Does anyone here have experience adding a superstructure to an existing frame to give the bike a new look without actually building a whole new frame?

I want to take a frame and dress it up and am curious if anyone has some no-no's or some must-do's to make this project work out properly. Thanks in advance!

adding things may well just constrain the material enough to cause a crack. There are lots of things you can do, but you have to be more specific. You might also look in the alt-bike-culture forum. Lots of mods going on in there.