It really depends on the context of the question, there's no rules you can use or memorize. I would say in general you can help facilitate the submission of a change request, but disposition of that change request is subject to your project's Change Management Plan. In my experience if a Customer has a scope change and the contract allows for additional compensation those changes are usually accepted.

Concur, CCB is final but when would a PM assist a stakeholder to submit a C/R if the stakeholder does not agree with the CCB and when does the PM just tell the stakeholder, just accept it (CCB decision).

This is a bit difficult to answer without more specific details. In general the customer would have agreed to the Change Management Procedures for the project (Change Management Plan). We always try to keep the customer happy, but also must keep in mind what was agreed to. We can always help submit a change request, but disposition would be subject to the Change Management Plan and CCB as appropriate.

How do you when help a customer submit a C/R if he does not agree with CCB or when to tell him all CCB decisions are final Both answers on two different questions were correct. How do I know when to do what?