Originally Posted by
Fursty Ferret
In this case by opening the fuel cross feed we're treating left and right wing tanks as one single tank. Makes no difference at that point which pumps have the higher pressure or if fuel moves between tanks.
If live engine pump pressure is higher then the purpose of using fuel from dead side is defeated. So follow the procedure and switch off the required pumps. There's no harm at all as the fuel from dead side is coming under pressure.