So, some 11 years after original post and still not implemented! I have supervised an installation for my neighbour and now need to isolate one zone from master valve as having to feed water supply from a different location using ShellyPlus1’s over wifi (for a roof garden). Neighbour very impressed with Rachio app 
I don’t want to leave main irrigation energised with no outlet, just asking for trouble! I am sure I’ll find a way around it but the option to disable master valve by zone would make my life a whole lot easier!
