I've always heard it's not good to make a rabbit eat less than they want. I know that certain things aren't healthy in excess (for example treats, fruit) but greens and hay (I guess pellets too, but someone else can tell that better than me about the pellets) can and should be available at all times. They won't make the bunny fat. It's important for a bunny to chew even to keep their teeth healthy.
As far as I know, bunnies know when they've eaten enough, my bunnies always had a lot of veggies and pellets available, and water of course. I think even decreasing quantity could be a bad thing..
it's my opinion..