Unfortunately I don't have an Aux Switch to tested myself. You’re going to need the manual for this:

Set up Program Transmit on Preset to Send PC 00 (M5: Preset 1), Page 50 of the manual.

Hold Encoder Go to: midi -> go to XMT MAP (press) got to -> 1:1 = 00

Connect your Aux. Switch , Default is Tip- Bypass. (once you connect on of the 3 switches should bypass the effect)

Set up XMT CC (bottom page 48) to transmit CC#11 to transmit on Tip

Hold Encoder Go to: midi -> go to XMT CC (press) got to -> [TIP>C11]

Now Save the PF on Bypass position.

When you hit the Aux. Switch it will flip/flop tape delay and Crystals

I don’t know if that works but another way would be to duplicate both presets; 1:2 PF and Preset 2 on M5. If you enable transmit PC save one preset with the PF on and M5 off then the other preset vice versa.