Here's the summary of what I have found during recent testings on FL Studio inserted inside BiaB.

Method 1: Change Note Velocity to Zero
Not working. Insert a note in the piano roll of the track in which FL Studio is inserted, and change that note's velocity to zero, is NOT going to work. When you render the song from BiaB, that zero velocity note is still going to make a weak sound, being not completely muted.

Method 2: Change MIDI Routing Settings
Working but complicated, not recommended. Changing MIDI input routing settings in FL Studio, so the note inserted in BiaB's piano roll is not making a sound when rendering, can be achieved, but messing with FL's routing settings is needed and not a pleasant thing to do.

Method 3: Hiding a Note in BiaB's Count-in Bars
Working. This is my preferred method.

Bottom Line
Having FL Studio inserted into BiaB as an external plugin and play VSTs inside that FL Studio instance syncing with BiaB, is a game changer. Because of this, I have already uninstalled RealBand and BBPlugin from my computer, and found no reason to install them ever again in the future.

A Canadian music producer, singer songwriter, composer, and professional guitarist.