Lengthen track and copy existing content into new bars in one step

I want to lengthen a track, let’s say from 2 bars to 4 or 8 bars - and immediately copy the content from bars 1+2 into the new bars 3+4 (or 3 to 8) - in one step.

Is there a way to accomplish this?

I often start with short track length and enter some content via step or live mode.
Later on I want to add some variations, but only every 4 or 8 bars - not in every bar.
But when I change the track length the new bars are empty at the beginning.
This should work during a live session, so there’s not enough time to copy/paste by hand.

Track + length + > to duplicate.

(And Track + length + < to halve)