BUR #18298 has been rejected.
mass update marchen -> marchen_(album) -marchen
The wiki as well as Wikipedia say that Märchen is a musical album by Sound Horizon band.
In order to prevent ambiguity, it's just a German word for "fairy tale".
Many copyright tags based on actual music albums already have *_album qualifier.
Somehow I don't think aliasing will be the most viable option for such tag with 200+ posts because there are some other tags starting with marchen_*. While renaming is impossible.
Updated