Sure you can do that for some moderate improvement, larger improvements involve greater cone area like for example doing 2 15s, if doing a larger than recommended box and tuning higher requires you setting up your subsonic filter higher to prevent sub bottoming out.
progress is slow but i got the port cut and in today for testing and 3 out of the 5 sub amps installed its enough for some low power testing /checking making sure the enclosure doesnt have anything loose etc
hopefully ill have enough time this weekend to get all 5 wired up and playing