How to configure a variety of assembly state in Creo Parametric

Flexibility used to be based on family tables, so whatever one could do with family table instances one could do with flexibility.

I think that means you need to make your top assembly flexible as well in order to allow the substitution of the sub-assembly flexible, automatically generated, instance of the clamp.

Years ago I tried to get PTC to have delayed evaluation on flexibility - that one would define a flexible characteristic and that would be on hold through the assembly tree until some level the user decided would be appropriate, using the default values until they were over-ridden at the desire assembly level. I think PTC never did that because the automatic family table instance system was so much easier, using existing functions within the program.

The same applied with Pro/Program - one has to create a series of assignments through the product structure to get to the level the change is needed.