Well, I just tested out this idea. I'll probably pay dearly for it (ie, reload everything) ...
but I just modified tags, and forcibly set new tags 'eq' and 'visual' to a value of '1'; which, at this point,
the value shouldn't matter, really. Sync'd with emptool, and; so far, no ill effects observed. No apparent easter eggs either.

2405 39b0 Intelligence\ Dream:
type = tune
artist = Synaesthesia
LastPlayed = 1014327290
length = 12902998
PlayCount = 98
SkippedCount = 0
title = Intelligence Dream
bitrate = vs181
codec = mp3
duration = 567229
genre = Rock
offset = 0
samplerate = 44100
source = Ephemeral
year = 1997
tracknr = 3
eq = 1
visual = 1

One noteworthy side effect of doing it this way, is that playlists can have eq and visual settings. For whatever that's worth. Of course, adding the tags, does absolutely nothing, but I think it demonstrates that some sort of extension can be done. Whether it's a hijack thing, or ...