If players donate to my project, and I later put a price on the project or on some files, I'd like to count their previous donations as payment towards it. Does itch let me do this?

I'm thinking about offering paid early-access builds of my game, with more content than the free demo. If the early-access build were $3, whoever already donated that or more should have access to the build, and whoever donated $2 should only have to pay $1 more.

We don't have anything like that right now, the closest you could do is have a sale condition that gives a discount on another paid project.