Hi @Misha,
Transaction level tags work the same in Excel or Sheets. Category tags are only available in Sheets (as far as I know).
Answers to your questions:
-
Yes in Sheets only - Docs: Using Tags in the Categories sheet
-
Correct, they are not related or tied together, simply two levels of tagging. If you incorrectly use the wrong tag you can simply change the tag.
Note: There are a number of other Tag topics you might be interested in at some point in time. Here is a search list of tag topics: Search help pages for Tags
also; an interesting thread on tag best practices Tags/Categories Use Best Practice?