If my wife of 25 years has asked for a divorce and she has moved out, can I change the door locks to prevent her from coming and going as she pleases?

To prevent possible problems down the road, my advice would be to obtain a temporary order in the court establishing who will have sole and exclusive possession and use of the marital residence, pending a final order of divorce.  Without a court order, either party has the right of access to the marital residence.