I've actually thought about doing such a thing. You would have to make it so the resonator could be secure and come on/off without messing up the pad. You could do this two ways: attach the spud/screw/bushing (depending on how you wanted to attach the reso) to the pad cup, or make the spud/screw/bushing sit on a flat washer with little spikes that press into the back of the pad to keep it secure (along with the adhesive used to float the pad). You would have to disassemble the sax to get to the resos, so each time you would be completely disassembling and then reassembling the horn.
Snapping them in would be difficult to do well unless you attached the spud to the key cup- unsnapping them if built otherwise would definitely mess up the pad. I'm not convinced that snapping them in/out wouldn't mess up the pad anyways.
Screwing them on (you could make the resonator the male or female end, wouldn't matter really) could be done either way, but into the key cup would be best I think. You would have to build the resonators so that the underside is smooth and doesn't have sharp edges, and perhaps even give it a little spray with teflon spray so that when you screw it in you aren't cinching the leather. You would have to put some sort of screw slot in the middle of the resonator. I'd vote for philips.
Once the system was installed, you could have a few sets of resos matched to your horn- different amount of coverage, of dome, of material. These would be reusable and would last a lifetime.
It MIGHT be possible to install such a system with magnets. One in the key cup, one in the reso. That way you could switch the resonators without taking the horn apart, just use some tweezers or a pad slick and a steady hand. It would be anybody's guess whether that would work in practice.
I'm game to try it- anybody want to pay me to make and install such a system on a repad or overhaul?