FabFilter

Multiband can work similarly but it's not quite the same as processing single band with biasing.

You could use existing tone controls (the 4 band EQ) and a simple switch that would switch the tone controls from "post EQ" to "Pre+Post biasing"

So to use existing 4-band EQ either as a postEQ tone shaper, or a biaser (-12dB pre-input, +12dB post output) - affecting only biasing not the overall spectral balance of the signal.

There's a few plugins on the market that do this (Softube Overstayer, Tone Projects Kelvin)

WHILE I'M SUGGESTING FEATURES:

Ability to use any band in FULL-BAND mode!

There's so many times i combined i.e. Smudge and Breakdown, and i always need to load two instances and macro them externally.

If i could simply switch both "bands" to full-band mode, i could use both in a single instance.

Smudge+Breakdown is an INSTANT transition maker, but it's such a pain in the ass to link two instances.