There is an undo button. MP3tag, on the other hand, cannot guess what other actions have been applied to a file before you load it into MP3tag. And even then it is not always possible to undo all.
You can select individual action (groups) either from the actions menu if you use the entries below "Actions ..." or select an action from the toolbar button. This is independent from the selection in the Actions ... dialogue.
Once you have all checkboxes cleared in the action list [Alt+6], then use the button "Utils" [Alt+S] and save this state with a name of your wish.
Afterwards you can reset to this state via the "Utils" dialog when you need it.