In Unity there’s not a real clean way to pull off such global informational “add ons” to user greetings – in Connection you can use the “route from next” feature to play this option for all forwarded inbound calls to remind them they can always press 0 to reach an operator at any time or the like (although I question if callers really need to hear this – understood customers can be rigid about such assumptions, however)
The post greeting recording feature in Unity is close (this is played after the custom or system generated greeting plays for a user or handler) – however it’s intended for legal disclaimers and user input is specifically disabled while it’s playing (i.e. forcing callers to hear it). So that wont work...
You can certainly have some canned greeting you paste into everyone’s personal greeting although the user experience there is pretty awful – the caller won’t know who they’re leaving a message for – I’d think this is far, far worse than folks not understanding that perhaps they can reach the operator instead of leaving a message by pressing 0 (or 2) during the greeting.
That said, you CAN lock users out of their greeting by assigning everyone to a custom key map conversation and removing the greetings section from the setup menu – this effectively means admins alone can edit greetings.
The 0 key is already mapped to go to the operator call handler in the caller input keys for users by default but you can bulk edit user input keys for users to send the 2 key where you like as well. Although again, 0 is probably the better choice - it's the usual operator breakout key.
