Actually it is not possible to replace a varied item in assemblies, without removing the flexible constrains.
If you use flexibility to show an assembled o-ring in the 3d, you must remove the flexibility to be allowed to replace it with an unrelated part (an different o-ring, no family table or something similar).
- But it might be that in Windchill, there are several copies of o-rings already available and they will all look same and have the same structure (as they are copies from a "master"-o-ring). After assembly, they all will have the same size, so can use the same flexibility.
- Same if you want to replace a spring to another one with different wire diameter, coils,...
Used flexibility is spring length (e.g. as an parameter and part of relations) and is all same for all springs in your company.
From my point of view, it needs to enhance the evaluation-function to flexibility-parameters.