My game is free at the moment but people have made donations. 

I'm quoting from the docs page on Download Keys

"We've described in detail what happens when someone pays for your project in the How buying works guide. One important thing to note: If someone pays for a project that is free (minimum price of 0), they will still get a download key. If you decide to add a price in the future they will still have access."

If I add a new upload to the same project and set a price for that upload only, will the people, who have donated, have access to the new upload  as well or do they need to make a new purchase?

A second question I have. Is it possible to send download keys only to people who have donated?

Forgive me if this has been asked before.