Open the BiaB song file in RB. (sgu, mgu etc)
That's quickest way, just make sure to Save As a SEQ file right away so you don't lose any work. Otherwise it may default to saving over the BiaB file.
If you have MIDI you want as audio, use the Render option to make it an audio track.

After opening the song, simply click Edit- Tracks - Make all tracks regular tracks.
Then you can edit to your hearts content without any worries.

Regenerate sections, cut/paste, generate new tracks, multiriffs etc

If you leave them as BiaB tracks, signified by Blue track names, regenerating (and generating) will take longer as RB will try to regenerate all the BiaB tracks all the time like BiaB does, but it isn't as fast at this.

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