I would not suggest to modify existing coord-systems, but to define new one you can use command _ADEDEFCRDSYS
HTH, - alfred -
The problem is that Autocad Map 2012 by default, performs a given geodesic transformation (between 2 datums) that is not valid (It is correct, but I need more precision). In my country (Spain), we used transformation grids (gsb) to make that change between two datums. If I could edit the default geodetic transformation would not have to create new datums, coordinate new systems, new geodetic transformation ... but as it is read-only ... thanks!