Changing the rules is very much in their control.

Congrats on winning the tickets. Should be great fun.

I'm with teemsteem on the point though, if you're going to make a contest, don't change the rules half way through. If you are going to change it, make it blatantly obvious give everyone the information.

Letting a raffle decide winners, a good way to run a contest. Letting community decide winners, also a good way to run a contest. Swapping from one to the other while the contest is running, bad way to run a contest.