RE: Sig Sealane sponsons
I am currenly building a Sig Sealane (very slowly). Anyway floats/sponsos are attached to the wing with a nylon bolt into a blind nut in the float so they can be removed for flying from land so yes it would be very easy to change the floats. The plans also show you how to build removable landing gear so you can fly from land. If you decide build it you might want to search RCU - there are several threads about adding chines etc.
Mark