There is no method to assign a new prop collection to a picker, but all methods are in place to modify the prop collection, and the prop collection itself is accessible for modification. This however requires iterating over a collection and making a ‘deep copy’.
Another issue is that I think the vtkAbstractPicker should have a GetMTime() that depends on the modification time of its prop-collection: at the moment it is possible to modify the prop collection without the picker being Modified(), while the picker’s own methods do call Modified().
My proposal is to add a SetPropCollection method and a GetMTime method, and adjust the current methods for adding/removing props (they no longer need to call Modified()).