Locking selection bezier handles on vertices

[tricky]

I've often wondered how to do this. If I have a rectangle, but want to edit two of the vertices by moving one of their bezier handles in the y-axis (or z, or whatever), how do I replicate the exact same bezier translation on the other vertice? You can't lock selection to just the bezier (as far as I am aware), and you can't type in a value for the movement of a handle.

[DanielBrew]

There's 'lock handles' in the 'selection' rollup of the editable spline. Does that do what you want? There's no typed input for bezier handles, it would be very useful though.

[AJ Jefferies]

It's possible to copy & paste tangents. Look under Geometry>Tangent when in vertex sub-object.