I have to say it .. ever tried Realband?
Makes what you are trying to do real easy. and more ..

It comes with BiaB so you probably have it.
Open Realband and open your song.
Highlight the section you want to generate, select a new blank track (of the 48 available) and generate a new part. When happy, remove the part in the original track and mix the new one in however you like.

Much more flexible and easier for this type of work.
Otherwise I can't offer much help; I'm off working in RB long before I get to the point of wanting one measure edits.

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