I run the game in ian mode
Wise move - "G" is so much easier to spell

Mmmm, interesting - when you say it crashes when you end the turn, is it as soon as you hit the button, or does stuff move about first, I wonder?

Murphy's Law would tend towards it being something like a tab or a comma or a quote mark in the wrong place, I guess...

So, what else would I check?
- region_specific - you have names etc set up for the new ones? That might conflict if you com out the startpos declarations. All your "region invaded/lost/conquered...." etc etc strings are consistent?
- MINILUKUP map consistent (though this is a surprisingly tolerant part of the mix...)? I expect this will be fine, as you've already gone past the FE_MINILUKUP to even start the game.
- no changes to factions or starting kings? Any owners of the new provinces? Any AI agents on the board in startpos? Standard start date?
- one trick I often use is cutting out all MakeBuilding and MakeUnit entries (though this is more likely to be related to a loading CTD), then try to narrow it down faction by faction putting stuff back in place...

Hope that helps you remember something you may have forgotten