Can you paint warming plate of an electric coffee maker with water based silicone epoxy paint?

No... i wouldn't. Even though water based paints seem harmless because of the reduction in odor, the substrates in the paints are dangerous and exposing them to heat is a bad idea. Water base paint cures in cool settings while oil bases dry w/heat.

The heating unit is most likely sprayed with the same type of paint that is used on engines and in fireplaces and are highly toxic.

I would just go buy a new coffee maker.