I'm not sure what you mean by "lock" a Datum CSYS. The default location is at, and orientated relative to, absolute space. If you accidentally move a CSYS you can edit it and change the 'Type' back to 'Absolute CSYS' and it will snap back to where it belongs.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA Siemens PLM: UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
You answered my question, thank you.
I guess it would be nice if the Datum Coordinate System could be associated to the abolute origin, in the same way that it can be associated feature data.