Cant remember if you can do this or not but see if you can assign L1 to macro #98 or #99. You can do it with L3 & R3.

Then you need to wait for 3.2 to come for the new commands, /hotbar next & prev

Or you could just use 2 hotbars for combat (you should be able to fit all the skills on) and enable extended hotbars. Removing the need to change.