In the Webmin Actions Log, under Action Details for a particular logged action, there is a "Roll Back Files" button at the bottom "to revert all of the modified files to their contents before this action was taken."
However, sometimes a single action details page can include many different files and commands. It may be desirable to roll back only one or a small subset of these actions, instead of having to roll back everything. This would be especially useful when trying to recover from a bug, such as Bug #658.
A nice thorough method to implement this would be to add a check box to each individual action on the page. By default, they would all be selected, and the button at the bottom would function the same as it does now. However, if someone unselects some of the options (and there should be an "unselect all" to make this easier), then the button at the bottom will only roll back those actions that were selected.