This adds 3 checkboxes under the "point-to-point" as []X []y []z. They're all selected by default (which is the familiar use), but you can deselect any so that when you click "OK" the deselected axis remains unchanged.
This would be especially powerful if additionally a button labeled "coordinate" would allow you to select a plane, or 2 orthogonal axes to redefine the coordinate system used when locking one or more of the axes. Understandably that will probably require another feature request so I'll be happy if just the first paragraph above was implemented.