I think Marc is correct. I also think that this section is a "out" for customers to specify something that may not be stated elsewhere, such as a generic performance specification or tolerance on a drawing.
We have had a couple of occasions where there was a new requirement for testing that was a result of a failure long after a product had been in production. Example, a customer is suddenly experiencing breakage, so we instituted a break test sample. This was added to our control plan. It is not necessarily stated anywhere on the customer's drawing or specifications, however.
If there is some requirement, such as a higher Cpk, you should have addressed this in
APQP, including a feasibility review, anyway. So requirements above the minimums in QS9000 and APQP and Control Plan manuals should already have been addressed.