I think your task is if not impossible, but at least very inefficient way of solving this.
Your institution must in some place parse the Swift messages to be able to act on them.
Besides the formal structure and rules of the Swift message itself, your institution surely have some kind of algorithm to match account numbers.
Account number can be erroneous, and probably altered manually by service staff. And I guess that you want to act on the valid account no that is actually used for the transaction.
So, my advice is work out some kind of access to/extract from the database that stores the pared messages.
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