Isolation of watch crystal from ICSP
Mike rightly says that the crystal is high impedance, but I would still isolate it since the maximum allowed drive level of these tuning fork crystals is usually 1 \$\mu\$W. That's for resonance, but I don't know what a high amplitude logic level signal will do to the crystal.

I would use switches with the lowest possible on-resistance. Routing seems to be more critical than I thought, then an analog switch in a 1.45 mm MicroPak, like the FSA1157, is better suited than a big reed relay.