I would imagine that most people when starting a project (especially if they have made enough progress to get a Kickstarter campaign going) would at least have put some thought into the rough price they’d be putting on the game (even if they didn’t have an exact figure they’d have thought about the ballpark price they’d be charging). It’s the kind of thing I would expect someone to have thought about, especially if they’re offering the game as one of the tier rewards (that suggests to me they have some thought put towards the game’s value).
I think if you released the game for a higher price later on, it would be very hard to convince anyone that you had no idea of the game’s intended price at the time you were offering the Kickstarter rewards. I certainly wouldn’t want to try it 