Create landmark at x,y,z. Modification of landmarks coordinates

A user asked me whether it would be possible to create a landmark at a given X,Y,Z location via a user interface (new window) instead of having to modify manually the .VER, .CUR or .STV files and loading the file.

It would be nice to be able to modify the XYZ coordinates (and orientation NX NY NZ?) of a given landmark via window, in a way similar as that already available for surfaces.
