Generally, a Power of Attorney (POA) gives the person receiving the POA, the ability to act on behalf of a person (also called a principal). It should be stressed that the POA gives power to the agent on behalf of the principal, not over the principal.
As such, the principal always has the authority to revoke their power of attorney, though this requires that the principal be of sound mind.
As long as the principal is of sound mind, they have the authority to revoke a power of attorney, modify or create the power of attorney, or appoint a new agent for the power of attorney.
Any change or revocation to the POA must be done in writing. If such a case has been made, it might also be a good idea to notify any person or institution that was dealt with by the previous agent.
A principal might choose to make decisions on their own behalf, assuming that they are of sound mind and mentally competent to make such decisions. As such, a power of attorney cannot override the will of the principal.
As such, there is a case if a durable power of attorney exists and the principal is no longer mentally competent, in sound mind, or otherwise incapacitated. Dealing with a legal document generally requires that a person be mentally competent.
As such, a person who’s not of sound mind may not revoke or create a power of attorney.
If a principal is unavailable or incapacitated, it can be complex to challenge the power of attorney and this might require legal intervention.
A family member of the principal may choose to challenge the power of attorney in some circumstances.
This can include circumstances where the agent doesn’t uphold their fiduciary duty of representing the best interests of the principal, or if the agent goes beyond or overreaches their authority.
The POA may also be challenged if the agent doesn’t fulfill their duties or otherwise becomes incapacitated or not of a sound mind.
Additionally, if a court determines that a principal cannot make decisions, the court may appoint a guardian or conservator for the principal. In such a case, the guardian may override any existing power of attorney.