Yes, she can change the locks at any time she chooses and she would be within her rights to do so. Additionally, since you left the marital residence, your wife can ask you not to return to the residence. If you come back after that (or even refuse to leave after she asks you to) you could be arrested for Domestic Criminal Trespass.
I suggest that you retain an attorney and have a proper Separation Agreement prepared immediately.
Robin F. Verhoeven
Attorney at Law
Rosen Law Firm
4101 Lake Boone Trail, Suite 200
Raleigh, North Carolina 27607
The response posted above is based upon the limited factual information made available and is not intended as a full and complete response to the question. The only reliable manner to obtain complete and adequate legal advice is to consult with an attorney, fully explain your situation, and allow the attorney sufficient opportunity to research the applicable law and facts required to render an accurate opinion. The basic information provided above is intended as a public service but a full discussion with an attorney should be undertaken before taking any action.