Legal Question in Wills and Trusts in California

No. A durable power of attorney can be voided at any time at the election of the person who signed it.

Furthermore giving a POA is not any kind of surrender of rights to make decisions. It is not the same as a voluntary conservatorship. All it means is that the attorney in fact has been granted the rights to do the same things as the grantor could do themselves. It doesn't mean the grantor cannot do them if the grantor is physically and mentally capable of doing them.