Yes, that should be possible. The sample playback starts at address 0 of the first chip, and if the playback address reaches the max address of the first chip, it switches to address 0 of the second chip.
You’ll have to study the code to do this. If your serial connection can send in a number, then playback can start at that address. Likewise you can send in an end address and stop at that address. It’s a little complicated because there are 2 chips, so I’d implement with only 1 memory chip to start.