In my business, every day guests are sent arrival codes via SMS at a time earlier than the scheduled time to trigger the SMS correspondence to them, as there is always someone who calls and asks for an early checkin.
In these circumstances you dont want the SMS to trigger at the designated time, as it has already been sent to the guest (not a good look to be sending it again and a complete waste of money sending a second time).
There needs to be either :
-a tick box when you're setting up the rules of triggered correspondence that says 'do not send if manually triggered/already sent'.
OR
-When you are in a reservation and you open up correspondence to send the SMS or email earlier than the triggered time, there needs to be tick box that says do not send again or over ride triggered correspondence for this form letter.

This button would be a way to manually over ride the triggered correspondence you just sent and stop it from going out because you already sent it!

This would prevent a guest getting the SMS a second time at the designated trigger time.