I'm not expert at this, but if I understand you correctly, the switch from 'film/inductive' to 'lever' was made to the ZFE controller by GS-911?
If so, this alone will not solve the problem as the current values received from the sensor will not make sense to the ZFE.
You firstly need to do the pin change on the ZFE plugs.
Then you either need to fit a lever unit to the tank and modify the wiring/connector to connect to the lever type. If it's not possible to fit a lever type to the tank, you can fit a resistor across the relevant 2 pins of the existing wiring.
In the latter case you will of course not have actual correct fuel level displayed but you would have gotten rid of the flashing warnings.
If my assumptions are correct and you need more info on pin numbers to be swopped and resistor values, I can let you have what worked for me in terms of not being able to fit a lever type into the tank, but only to fit a resistor to fool the ZFE unit into not displaying warnings.
Good luck and keep us posted.