Yes, you can. I do this to control my backing tracks.

You need to have your HD500 connected through a MIDI interface (not through the HD500's USB port) and assign footswitches in your patches to send MIDI data of some kind (it works best if you're not using those switches for anything else). I use a Note On of the lowest possible note for all four switches I'm using for MIDI control, with specific velocities of 1, 2, 3, and 4 to differentiate them.

Then, in Logic, go to Key Commands (option-k) and find the thing you want to trigger. In the lower right there should be a button that says "Learn MIDI Assignment." Click that, press the footswitch on the HD500, and then click it again.

I found that, to avoid double-triggering, you sometimes need to do the following when teaching Logic which footswitch should do what:

1. Click MIDI Learn in Logic.

2. Press and *hold* the HD500 footswitch.

3. Click MIDI Learn again to make Logic stop "listening."

4. Release the footswitch.

Hope that helps,

Matt