Heya,
changing the Genre will be written to file indeed, it is part of the ID3 metadata definition for mp3s... which then would trigger a re-sync to cloud, if you manage your music that way.
MusicBee does have virtual-tags too though which do the same, and which only sit inside of MusicBee and aren't written to the file.
I do not use them however, but there is a fairly extensive twiki for musicBee where this should be covered.
c.
ps there's also an inbuilt way to manage podcasts differently from music in MusicBee - I do not use that either though, I only know it exists, and potentially you could funnel your audio books through there as well, instead of using the tags/virtual-tags method & smart-playlists.