Water with lots of washing up liquid works. It doesnt damage the rubber but the solvent in the silicone spray might cause the rubber to soften and or crack with time.
if all the above fails, cut them off and buy some new ones, (buy the new ones first of course lol) theyre not very expensive things...
But ive never had a situation where you cant get them off.
Is alot easier if you detatch the exhaust pars in question from the rest of the exhaust system so you can move it about free of the rest to get a better change of getting it off the rubber parts :idea: