It seems like 'metadata:' configs do not support the use of templates, like 'collections:' and 'overlays:' sections do. It'd be nice if they did as writing non-templated metadata configs for a mass collection of shows/movies can start to become unwieldy quickly.
The documentation is very unclear about Metadata edits not supporting templates, as they are both listed on the same 'metadata' file page, so it seems logical that it would follow the same sort of configuration as collections may.