As for the serial number issue you've mentioned a couple times now ..
Serial numbers are good for 3 installs on 3 separate systems. If possible, disassociate one of the machines to free up another license. Under 'Help' there is a Utility for this. If that doesn't work, call/chat PGMusic and have them free up the license or authorize another install. I know of both options working.

As for the 'RB regenerates everything' issue; there is a check box in RB config (I think it is under the Prefs-Song Generation tab) that tells RB whether or not to regenerate an MGU file when opened in RB.

Then also notice that when you open a BiaB file in RB, it is likely the file format will cause RB to treat the first 8 tracks or so as BiaB tracks.
They will have blue text in the track name to let you know.

When they are BB tracks, RB tries to act like BiaB and will regenerate all BiaB tracks when Generate is invoked, which takes longer in RB because RB generates everything before starting to play .. whereas BiaB generates just enough to get going, then continues generating behind the scenes as it plays.
So BiaB is faster.

To change this 'BB track' behavior in RB use Tracks-Make all BB tracks regular tracks. Then you are back in familiar RB territory. Only selected parts regenerate. No surprise regenerating.

BiaB = very quick chord/style/tempo creation over RB
RB = better editing/regenerating/tempo control over BiaB
plus RB has more tracks to work with, multiriffs, multiple audio/midi ports, etc.

BiaB is faster for what it does. When you start feeling stifled in BiaB, RB offers some relief.
When you feel stifled in RB move it to whatever you are comfortable with.

They are all just tools.

I do not work here, but the benefits are still awesome
Make your sound your own!