I’m new here, but…
Could you assign each master to it’s own station (not using the master station option that is built in). Configure both not to use weather adjustment, leave the city water station in a disabled state.
Then program both master stations to turn on a minute before your watering schedule and turn off 5 minutes after the schedule would normally end if there were no weather adjustment.
This way, you can set your lawn and garden to weather adjust and they will water from the pump. On those days the the well is low, you can log in from anywhere (your couch with beer in hand) and disable the pump station then enable the city water station.
At least, I think that would work.