Endpoints are defined in the service definition file (csdef
), so you need to modify this locally and redeploy the package.
That said: Endpoint modification isn't something that causes a delete+redeploy, if you push your deployment as an update (see this post on in-place updates). You can add and remove endpoints, as well as modifying existing endpoints, as part of the update (just make sure you don't actually do a re-deploy, as this will take down your deployment, dispose of the reserved IP address, and acquire a new IP address).
EDIT
My advice (to avoid a bad uh-oh moment): Try doing this on a test deployment first, to make sure you have everything set up correctly. Maybe push a test web app up to a new cloud service, with two instances, app on port 80. Then add an endpoint and push up an update (maybe even with updated text on the home page of your test app). During the update, continue to visit port 80, seeing that the app continues to run, and that the home page eventually updates. During this entire time, verify that the IP address remains the same as before the update.