I'm pretty sure PGMusic products use the same Elastique software to change pitch/tempo of audio as it does to generate it in the first place. At least RB does ..

This is much improved from a few years back.
Changing the key of audio in RB is pretty simple and painless. I've not tried in BB, not sure if it is as easy as RB or not.

May want to try opening the BiaB file in RB, then change the key .. at which point RB asks if you want to transpose the audio tracks too (actually it gives you a few MIDI/Audio options like excluding any track with the word 'drum' anywhere in the name).

As you mentioned 'Save As' another name to preserve the original.

You may notice artifacts, you may not, but it is easy to do what you are trying to do by using RealBand instead.

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