Hey guys, pretty newbie question... I've been playing guitar forever but never learnt how to set up my own guitars (never trusted myself or understood much about how to tweak things). I recently bought an Epiphone Sheraton II second hand to pimp out with new pickups and electronics... I have a vague grasp on how to rewire guitars, but I was also wanting to put 12-54 strings on it because I'm currently going for heavier strings on all of my guitars (I prefer the stability and feel of heavier strings, plus gives slightly clearer/chunkier tone imo).

This guitar is currently holding 10's rather well, with a few intonation probs on the G and B strings... I have a vague idea of how to fix intonation, but if I was to whack on a set of 12-54's what exactly would I need to tweak to stop the guitar from snapping?

The guitar won't actually snap. I'm not sure if you were being serious about that or not. You'll probably have to tighten the truss rod to balance out the heavier strings, but your intonation probably won't change that much. If it's all right now, there's a decent chance it will stay all right, at least in my experience.