Hi.
Once the rotation in done and the corresponding position of the rotating axes are rotated, you cannot set the datum. (I don't know why you want to do it)
Anyway if you need to do it, you need to change the kinematics of the machine.
The bit5 of the MP7500 in the KINELIST.TAB must be set.
When it is set you can set the datum after rotating of the 4/5 axes.
Remember to activate the Kinematics before trying. (one easy way is switch off/on the machine)
Jukka