Question on device selection ++

I’ve got a couple of things I just can’t wrap my head around here. I’ve managed to assign a button on my MF Twister to select the first device on the selected track, easy-peasy. But I’ve got a custom effects rack that’s always last in my chain, and I’d like to be able to select this device by pressing a button, regardless of how many devices are in my chain. I would also like to have a two buttons (or a knob) to move device focus left/right, but I can’t figure out how to do either.

Any tips?