What Mac said . . . .

If I need a song specific hook, I import it from a midi file and use the .seq function, or I simply record the part to either M or S track.

An imported midi track will NOT regenerate, so you are dealing with song layout, chord structure, and the Biab style when you press the play button to have the Biab backing parts "line up" with the imported midi track.

OR

Import the original midi file into RB. Then erase all of the backing parts and save the specific hook part(s). Then generate your backing parts "around" the specific hook part(s). Be sure to double check the chord layout prior to generating any RB parts though

Trax