Musicbrainz currently has an artist <-> label relationship called 'Creative Persons', which presumably identifies artists who utilize that label for publishing, production etc. I can associate artists with the label using this relationship type.

However, it appears that once I've done so, the relationship does not appear on the Edit page for the label. Consequently, there is no means by which I can alter or remove the relationship once it's in place, at least via the label. (The converse relationship is on the artist, and does show up on their edit page where it can be altered or removed).

Example: Middle Kingdom Music, Ltd details at https://musicbrainz.org/label/d39c77c0-cf60-4aec-8f7b-8456525a42b2/relationships shows artist Barney Bentall as a Creative Person, but if you check the edit page https://musicbrainz.org/label/d39c77c0-cf60-4aec-8f7b-8456525a42b2/edit the relationship does not appear.