Before you do the replacement, check that the part numbers on the ECU's are the same.
You can also check if the ECU's are like-for-like by going onto the Lings Honda website.
Here is the link
As you are in Dublin, I would think it best to enter the VIN. Do this for each car.
For each car, you should get to a page
like this. Choose the "CONTROL UNIT (CABIN)" section.
You should get to a page
like this. The ECU is item 3.
To get the Honda part number, you have to delete "_pfk" from the URL in the address bar and then hit enter. When you have done that, the page looks the same, but the Honda part numbers are now listed instead
as here. The ECU is still item 3, but now you have the Honda part numbers.
Note that a new replacement Honda part number on Lings might be different from the part number on the "old" ECU in the car. This does not matter, just make sure that the part numbers are like-for-like in the cars, and/or like-for-like by VIN on Lings.
I have never replaced an ECU, so I don't know exactly what you need to do, but if you find a difference between the Honda part numbers on the ECU's in the cars, and also a difference between the Honda part numbers for the VINs on the Lings Honda website, then you might be in difficulty.
IMO and with hindsight, it might have been wiser to check the ECU's first, and if they were the same, swap them first rather than swapping the engines.