It does take some tinkering. Running unadulterated, it's either a cakewalk or a nightmare, but nothing in between. My suggestion is to track the functional levels of your 'competitors' and make sure that even when you port over, you're staying within the game's capabilities.
So for instance, don't port over a game where, say, Lithuania from CK held every title on the atlantic coast. The game can't handle that; it's beyond the pale.
So instead, give away all those titles, and keep a few - Lithu-Poland-Balta, for instance; and then save and load up a few times as other nations with heavy use of the f12 key to 'gerrymander' a few of the kingdoms so the game can handle the conversion. So when you convert, you can offload the specs, and copy/paste the sections needed to a *new* EU2 game - -
because if you don't, the events won't fire
and a game without events is no game at all. Sadly, that's the best way to do any conversion - you have to spot-check the converted file against what a new game would look like, otherwise, you'd get a Ricky game where North America was still colonies, where Austrailia was still unsettled, and Micronesia undiscovered.
So for instance, my Ricky Mexico has a fair bit of industry - and so when I convert it all over, I want the appropriate level of people, of TC, and of raw materials to account for that.
etc., YMMV.