Is it possible to prevent for a certain user group to restore a document from the version history?
There are two permissions regarding Versions
- View Versions
- Delete Versions
If the user has only View Versions, then they cannot restore a previous version. However, if they have Delete Versions permission, then they can restore also. SO you may create a new Permission level and make sure that Delete Versions is unchecked. Then assign this permission level to the group.