I have read discussion deep in a thread that you take both flight computers offline by pulling the breakers. This reverts the flight controls to mechanical law backup. The side stick no longer works. Instead the rudder pedals and trim are used to control the flight surfaces.
Not so.
The FAC's are switched off by using the switches on the overhead panel.
The sidesticks will work perfectly
You'll be in ALTN Law with protections lost. Direct Law with Gear Down. You will NOT be in mechanical back up.
If you were to turn off all ELACs and SEC's you will be in Mechanical Back Up.