Is it possible to have a stretch handle enabled/visible to a condition, such as a layer visible?
Presumably, in the PCell you would only call the rodAssignHandleToParameter() function when the test condition is true, otherwise don't call it. Is this what you mean? The visibility of the stretch handles is controlled by the Options -> Display -> Stretch Handles item, or the associated .cdsenv variable
layout displayStretchHandles boolean t
I'm not sure that you can make handles individually visible, but you should be able to create or not create the stretch handle as indicated above.
Hope it helps.