Carbon Frame Respray

How hot is a stove?

The carbon fiber will be fine. But its relationship with the epoxy binder will be heavily stressed at over 150C. Much over 200C, and the frame could start to crumble.

Thats just my educated guess. I'd love to try it, and see.

But how can Mercian even offer this? have they done it before?

+140c for 20 - 30 mins for stove enamel,some carbon frames have internal plastic lugs.
You can low bake and use 2k paint with no problems,the hardest part of refinishing carbon is getting the old paint off without damage the rest is actually easier than painting most steel frames.