If you get an HD Retrovision Genesis model 1 to model 2 adapter (for use with their component cables), you can make the process of switching a LITTLE easier, but you still have to move the connection from the front to the back.
The way that would work is to use the HDR adapter between the Genesis and the 32X model 2 passthrough cable. Then you can quickly disconnect the AV cable from the 32X, disconnect the 32X passthrough cable from the adapter, remove the 32X from the Genesis, and plug the AV cable into the adapter. That's still a pain but not as big of one as doing it all from scratch.
The downside is that if you're using a SCART cable, you lose stereo audio this way. You only get mono from the DIN.
And when it comes down to it, the easiest solution might just be to get a second Genesis and associated cables, and swap the cartridge.