is there any way by which we change the presence of other contacts using ApplicationEndPoint, one way which i came across was to create a UserEndpoint and then make presence related changes, but that required credentials to establish UserEndPoint.
You cannot publish presence from an Application Endpoint, you will need to create a UserEndpoint using the SIP uri of the Application Endpoint, and then publish presence using _userEndPoint.LocalOwnerPresence.BeginPublishPresence()