The Policy Installation History is where you can revert changes on the Gateway level. This is how it works in R80.10 and R80.20. We are planning Management-level revert mechanisms, but they will not make our next release.
Let's give an example with R80.10 (and R80.20):
1. You make 50 changes and install policy
2. You have network drops
3. You immediately go to Policy Installation History, install a previous revision, the network was restored, all employees can breathe. Management configuration is still the most recent one, and includes the 49 changes and the 1 misconfiguration.
4. You go back to the Policy Installation History in order to see audit logs per change. You find the bad change, and do the reverse operation on the 1 bad change. Publish, install policy.