This is the only information I had on changing VO:
http://www.canadavisa.com/canadian-immigration-faq-application-process.html
5. Can my file be transferred from one Canadian Immigration Visa Office to another?
Under the Skilled Worker category, applications must first be submitted to the Centralized Intake Office (CIO) at CPC-Sydney in Nova Scotia. The application will then be transferred to the Canadian Immigration Visa Office outside Canada that is responsible for the country where you are residing (if you have been lawfully admitted to that country for a period of at least one year) or the country of your nationality. Applicants are responsible for indicating the correct visa office on their forms and marking the incorrect visa office may result in the return of the application.
Under any category of Canadian immigration, a request to transfer your application to another Canadian Immigration Visa Office may be made to the Canadian Immigration Visa Office processing your application. The latter will decide, based upon "program integrity", whether or not to transfer your application. In certain circumstances, the Canadian Immigration Visa Office processing your file may decide on its own to transfer your file to a different, more appropriate Canadian Immigration Visa Office, even without a request.