Renames an existing broadcast. The authenticated API key selects the account. This operation is rename-only. suppression_uuids and actions used to be accepted here and no longer are: sending either one returns 422 and the rename does not happen either, so the request has no effect at all. Set a broadcast's suppression lists with set_broadcast_suppression_lists and its tag actions with set_broadcast_tag_actions. Each takes the field it is named for in the same shape it had here, except that the field is required there rather than optional. A caller that used to send all four fields in one call now makes up to three calls.