FYI, this is also addressed in Mp3tag v3.35-beta.2:
[2026-05-22] CHG: Discogs Tag Sources: use Discogs convention of "Various" for various artists.
I'm using a slightly different replacement, which replaces VA, V.A., and Various Artists while ignoring case.
$regexp($if2(%albumartist%,%artist%),^(va|various artists|v\.a\.)$,Various,1)