https://musicbrainz.org/relationship/e6159066-6013-4d09-a2f8-bc473f21e89e has been used for all label reorganizations of any kind (excluding "parent label / ownership" changes). I think we can do better than vaguely describing everything as a "rename" with 2 common concepts that are more specific than renaming:

1. label absorption. e.g., Warner Classics absorbed EMI Classics (EMI Classics was absorbed into Warner Classics). The label being absorbed should be ended, and the label doing the absorbing should have existed prior to the absorption.
2. label split. e.g., Ariola Japan Inc. was split from BMG JAPAN INC. (BMG JAPAN INC. was split into Ariola Japan Inc. and Sony Music Japan International Inc.) In this example, the label being split stopped existing, the first target label did not previously exist, and the second target label previously existed. If we only want "label split" to be used for targets that didn't previously exist, then,
   • business transfer. e.g., BMG JAPAN INC. partially transferred its business to Sony Music Japan International Inc. (Sony Music Japan International Inc. partially absorbed the business of BMG JAPAN INC.) In this example, the label transferring its business stopped existing, but it's common for businesses to transfer their business without going out of existence.

Date guidelines are the same as label rename.

("Label merger" isn't included here because what commonly happens when two labels are "merged" is that they become parts of a new parent company.)