You can use an Action to do this. Action are what I like to think of as Webhooks for Dummies and I will take a dummies solution over complicated syntax any time I can.
But one trick is that on first look, it will not appear that an Action can edit the record that you are on. I seems to only have functionality to add a record on another table or else edit "child" records.
But you can create a Report Link field type on the Record and connect the [Record ID#] on the left side with navigating to the same app, same table same [Record ID#] field on the record you are on. That is allowed to be your Report link field for an Action.
Then set the Action to fire only when the [New True ABR#] changes and after the save the [New True ABR#] is not equal to the [ABR Number]
Give it a try.
Note also that the Action, like a webhook, will fire a split second after the record has already started to re-display on the screen after a save. So while initially it may seem that the action did not fire, in fact if you F5 refresh the screen in View mode, you will see that it did fire.
