Just my dime and just how I do it, when I lay the chords out, I add and extra 40 measures to allow for expansion. And when I start approaching that, I add 40 more. Then when I know I am done with chord layout, I go back and delete the excess from the end. THEN generate the song.

What function are you doing where you want to select the whole track? Regenerating it? If so, maybe just add a blank and generate it fresh, because you would then have to "ideas" and you could cut and paste as you like and seam them into one good track. I found RB to be a whole, great new world once a group of people taught me how to use it. One of my songs has a tenor sax solo that ended up being pieces of 4 solos stitched together. Track 12, 13, 14 and 15 are all solos and I took a little of this and a little of that and pasted them on 16. When I had what I wanted I muted the other 4, voila...