> you can't undo a note, can you?

Probably no, mostly because you cannot uncreate it.

> I have disabled auto upload

In such case if you are curious about tagging being used you can experimentaly tag something and undo edit without extra tags.

In some rare cases quest will not come back but in general you will be still able to answer it (and rescanning for quests will get missing quests back if you have not uploaded answers and noone else edited relevant objects)