Yes you can change patches over USB. Just enable Axe MIDI Out in your MIDI editor or DAW and send program change messages to this output. Program Change (PC) messages range from 0 to 127. If you need to access more than 128 presets, use CC#0 to change banks. Then the PC messages will select the corresponding preset in that bank.
CC#0 value 0 = Bank A for presets 0 through 127
CC#0 value 1 = Bank B for presets 128 through 255
CC#0 value 2 = Bank C for presets 256 through 383
CC#0 value 3 = Bank D for presets 384 through 511 (XL only)
CC#0 value 4 = Bank E for presets 512 through 639 (XL only)
CC#0 value 5 = Bank F for presets 640 through 767 (XL only)
Keep in mind that if you have display offset set to 1 in the Axe, the display numbers will be one more than the MIDI PC message. For example, with display offset set to 1, PC# 127 will bring up preset number 128 on the Axe. Also, if you have any preset mapping setup in the Axe, it will also follow whatever mapping you have setup for pulling up specific presets or scenes.
If you want to trigger Program changes from the Axe (like changing a synthesizer patch on your DAW when you manually change presets on the Axe), turn on USB Adapter Mode in the I/O menu and enable Axe MIDI In in your DAW or MIDI editor. Then any Program Change messages processed by the Axe will be sent to your DAW. You'll have to set your MIDI track or soft synth or whatever to listen to the proper channel on Axe MIDI In for it to respond to the incoming messages from the Axe. Keep in mind that the Axe is passing the PC messages from your MIDI foot controller and will not send PC messages for front panel preset changes. In other words, the Axe does not create MIDI PC and CC messages, but rather echoes the ones it received from a MIDI foot controller to its own input.
