Does anybody know how to sperate the lense from the housing on s4 tail lights without destroying the lense?

I THINK you can use a heat gun to soften the adhesive, but wait for someone else to confirm that.

bake them in the oven that is the best way to do it. it gives you even heat on the adhesive and prevents from localized burning from the heat gun. i think the temp you need to put the oven at is like 200* let me double check i will get back to you.

250* to 300* should do it and put it on a block of wood as the metal rack can leave marks on the light fixture. and only like 5 minutes max.