What happens to existing free users if an App gets moved from free to paid? Hey I have a free app in iTunesconnect that's being downloaded about 100 times a week. Mostly no user responses, no support requests or anything so I thought (I know this is selfish) I can make some free money by making the app worth $.99 so maybe some "accidental" buyers are too lazy to refund it.

Now the thing is: I still want users who downloaded the app for free continue using the app for free - is that possible as the transaction is already on their iCloud account? Or will they be asked to buy the app as soon as they try to install it on a new device?
The user buys an app for the price it is sold at that point. Future changes to the price have no effect on them. It is on their Apple ID that they own the app and they will be able to download the app for free as long as it's available (no matter the price).