I would rephrase this as

1. Support the new value in your schema

2. Support the new value in the client

3. Emit the new value from the server

Combining 1 and 2 is probably possible, but not a great idea. Imagine if you end up rolling back 2 and 3, but there are still potentially new values in flight. If 1 is still there, you're good. If 1 and 2 are combined, you rollback all 3, but the new value is still in flight and your client crashes.