As I understand it, once you are in the context of a transaction everything you do (like SEND, COMMIT, ABORT, and ACK) has to be in that context.
So, in your example you would have to send your message in the context of transaction TRAN03, like this:
this message should not reach the destination
In that case if you abort you will have sent the message "this message should not reach the destination".
"SEND" outside of the context of TRAN03 is not committed to adhere to that transaction.
Have I understood your question or were you talking about something else?