just heat up around the edge using a hair dryer if you want to take them apart, the problem with the MK2's is that they are a clear lens and they are coated with a clear coat, which over time gets stone chipped just like the rest of the car and cause its plastic it is damaged much more, i have found using a polish with a slight cutting compound in it works, super resin polish, megs scratch x, megs plastic x are also good ones to use, but the best way is to machine polish them, as this will generate heat and soften the lens and cuts back the clear coat
here is a pic of a head lamp i have machine polished:
Before: