Run a stepper from 2 DM542 drive

[gabi68]

The fiber laser has a board called DLC2-M4-2D which is a 2 board connected with pins. The top board is a controller for X,Y,Z,A axis (can drive a Z axis, a rotary axis, an XY table and all the combination between). The bottom board is dedicated to run the laser head itself (2 small servo motors connected to 2 mirrors to steer the beam and stop it and start it depending the user design).
The top board is a step and dir controller and is connected to a stepper motor which operates the Z axis
I also have a device (with his own stepper driver) which has a measuring sensor for the focal distance (different lens have different focal distance) and this device needs to use the same stepper motor on the z axis.
This was my question: how can I change the drivers (safely) to use the same motor when I need to use one or the other device?

Thank you
Gabi