If you import Trakt Ratings to your TMDb account, does that replace your TMDB ratings? Edit: (i.e. if I rated a movie on tmdb as 6, but I rated it as 8 on trakt, will the rating change to 8 if I import my trakt ratings?)

Hi @tmdb24407783, if you run more than one import (from any source) and the rating already exists on TMDb, it is skipped. We do not overwrite your TMDb rating with a CSV import. The system is designed to support many imports and it would not be very nice if you were tweaking the data here only to have it overwritten by an import. Although I suppose one day that could be a option (to overwrite or not).

Edit: Also, how would one import ONLY movie and TV series+seasons ratings (i.e. exclude episode ratings) from trakt? Would I have to manually change the csv file? (haha, I would have to learn)

You would have to manually change it. The importer simply tries to match all of the IMDb Id's found in the file.