I have imported a deck with multiple tags which are not grouped together (as in by using hyrarchical tags). Is there a way I can do that myself (for less clutter)?
I tried renaming one of them from N1 to JLPT::N1 but it just creates a new tag instead of modifying it.
Renaming them should work (as long as you use the exact same text). What you did should move the N1 tag under the JLPT tag, and will create a JLPT parent-tag if it doesn’t already exist.
Hmm… I tried it in AnkiDroid but it just creates a completly new tag. I didn’t realise it then but now I think I can just replace my old tags with the new ones. Thanks for your assistance still!