In your example you stated that an change request is approved for new quality criteria, despite the deliverables being validated. Here are my comments on the three options presented:
a. Go ahead and transition the completed deliverable to the client
This is not the best option. This option ignores the fact that a change request has been approved. Remember, the change request was approved by the CCB for a reason. As a PM you should be proactive and address change ASAP.
b. Hold off on the deliverable transition and apply the new approved quality criteria on the deliverable
c. Apply the new approved quality criteria only on future project phase
In my opinion, both b and c have the potential to be correct depending on the specific circumstance in the question. However, I believe the most correct option is b for this questino. The question did not state that the deliverables were accepted by the customer. If the change request was approved, I would assume the CCB approved it with an understanding of the potential impact on cost and schedule. It may not be correct to apply the new criteria only in future phases as this could result in your new deliverables not meeting the requirements (e.g. the new quality requirements) expected by the customer.