Users get an error message when they try to do either of the actions for refunded Apps.
Update Unavailable with This Apple ID
The App Store no longer allows people who received a refund to reinstall or update the app with a clear message: pic.twitter.com/zR5drjVCke
— Michael Simmons (@macguitar) May 24, 2014
This update is not available for this Apple ID either because it was bought by a different user or the item was refunded and cancelled.
In the past users could re-install or update an App for which they had been given a refund. To get the refund user has to first report the problem with their purchase and then select the option to request for a refund. This new step has also been been extended to the Mac App Store.