sharepoint programmatically change master page

SPSecurity.RunWithElevatedPrivileges(delegate() { using (SPSite site = properties.Feature.Parent as SPSite) { using (SPWeb web = site.OpenWeb()) { //Logging feature activation status in list web.AllowUnsafeUpdates = true; //Changing the master page web.CustomMasterUrl = "/commerce/Custom/_catalogs/masterpage/Custom.master"; web.MasterUrl = "/commerce/Custom/_catalogs/masterpage/Custom.master"; //Setting the Navigation propertiers for web web.AllProperties["__IncludeSubSitesInNavigation"] = "False"; web.AllProperties["__IncludePagesInNavigation"] = "True"; web.Update(); } } }