As an alternative I would suggest to use
Format string: $replace(%genre%,Mumble Rap,Hip Hop,east coast hip hop,Hip Hop)\%_filename%
with an increasing list of pairs to replace.
The identification would have to be done by the user.
So I wonder what would be faster: let the original action run and then scan through the list of folders and move the files manually or scan through the list of genres and adapt the filename generation action each time a new subgenre is found.
In general: I do not think that arranging files by genre in the file system is a good idea as this is a classical task for the player. Modern players also support multiple genres, something that the filesystem most likely will not.