Yes. As long as you are mentally competent, even if you have given the power for your agent to act immediately, you may still make your own decisions and conduct business on your terms. If your agent does not respect your wishes, you may revoke the Power of Attorney.
Problems may arise, however, if an agent with a Durable Power of Attorney believes you lack the mental capacity to act independently or revoke the Power of Attorney, but you disagree. If this occurs, a court proceeding may be necessary to determine whether you are of sound mind.