The authority of the change control board is inherited from the authority of its members, who are usually influential stakeholders. This means that any decision taken by the change control board has to be executed as is: the decision to whether accept a change, reject a change, or cancel a change.
As a project manager, all you can do is explain (objectively) your point of view to the CCB if you think they're taking a decision that will have disastrous effects on the project. You can never ever force your opinion on the CCB, or refuse to abide by the decision of its members.
While answering your question, I would like to discuss how a change control board takes a decision. There are mainly three ways:
- Consensus Voting: Where every member of the CCB has to vote "yes" for a change to be processed.
- Majority Voting: Where a change is processed if it receives a majority of the votes.
- Voting Shares: In case of very large organizations and very important programs, the number of shares that each member of the CCB counts (in this case, the CCB consists of the major stockholders of the company). For example, if someone has 51% of the shares of the company, then he can get any change he wants processed. If two CCB members with a combined stock holdings of 60% of the company join efforts, then they can also process any change they like.
Note that it is possible for a key stakeholder (such as the President of the company or the CEO) to have veto rights. For example, even if every other members decided to process a certain change, if that key stakeholder votes no, then the change is blocked.