Oh, now I see. In "ABCD" mode FS5 - switch becomes "A" - switch. When you hold the MOVE button for a while, you can assign a Midi Contoller to FS5, but not to "A". Take a look at the manual page B5: "USING POD HD500 as a MIDI Controller device". " Note that footswitches FS5 - FS8 will only transmit your configured MIDI assignments when their Setup option is set to the FS5 - FS8 “Pedalboard Mode†" In ABCD mode you must control Midi Sends over FS1-4, so you cannot switch to another preset and send a Midi command at the same time. Instead of changing a preset you can only turn on/off effects. This will always need 2 kicks. Example: FS1 = Clean amp channel; FS2 = Crunch amp channel; FS3 = chorus + delay on/off. Practice: FS1+FS3; FS2+FS3.
But there is no advantage. You can also change the preset over ABCD and then change the amp channel over FS1-FS4 or vs.