...there was some way to change your rating. I just played a level that I really didn't like on first play and so gave it a thumbs down, but the more I thought about it, and then went back and actually replayed it, I'd completely changed my mind and would've now given it a thumbs up.
There isn't some secret hidden way to change your assessment, I'm guessing?
Unfortunately not once you have made your vote it stays that way & remembers, you don't get to vote again.
You would think the whole purpose is to improve where necessary so any negative feedback could bring change which in turn should make the experience better.
With some of the other Far Cry games you got to vote every time you played the map so I guess if you played the same maps over and over you could vote them up and keep the rating high (I am speaking more with Far Cry 2 here which was multiplayer only)
Looking at that option it would at least mean that people are repeat playing which surely is better than just playing only once so maybe some multiplayer maps could have fabricated ratings but again at least they are playing the maps over and over to get those ratings which keeps the game healthy if people are playing.
If they allowed a map to be re-voted on after going through the editor again and receiving an update that could be prone to abuse some could simply move items forward / back and edit terrain then replace similar to how it was and not really do a lot just so they could vote the map up so no matter what scenario / options the player gets there would be some looking at abusing for their own gain.
Still if they are to keep the ratings system maybe allow votes to be cast every time the map is played, it is for Ubisoft to filter out the better maps and do a better job showcasing peoples work and supporting map builders better than they have been doing so people can find work by those who are dedicated and excel in creating maps for everyone to enjoy.
In short I agree it would be nice to get the option to change your vote or cast it again.