MBS-7489 ("Artist Credits for Relationships") supports different credits for one artist on a release, typically a performance name and legal name for composition relationships. When editing artist relationships we currently have the "Change all relationship credits for <artist> on the page" option. If we had a change similar relationship credits option it would support these different credits / one artist situations better.
Options for "similar" include recording/work etc. or relationship group (e.g. composition, production). The latter's probably better as arrangement and production often get legal name credits.
Interface-wise you could leave the single line and have a drop-down box to choose all, ... in which case you could have several options I guess.
http://musicbrainz.1054305.n4.nabble.com/STYLE-534-When-to-merge-artists-tp4673837.html