Steppers on a manual mill

I am converting a manual mill with steppers geared 2:1 to the lead
screws and am keeping the manual capabilities also for now.
My question is do i need to disconnect the steppers from the lead
screws when in manual mode or maybe disconnect from drivers?
Wondering about steppers generating a voltage when moving manually
especially when using the power drives on the X and Y axis.
The power drives will move the table at 45 inches a minute in rapid
and the steppers are geared 2:1 to the screws so the stepper
motors will be turning twice as fast as the lead screws.
Can they generate a voltage that will hurt the gecko 201 drives?
Will it hurt the Bi-poller steppers to turn then like this?
Thanks for any advice!