First thing I would do if in your shoes - and assuming you don't want to do this while it's in your TomTom - would be to find a card reader or SD to USB dongle and get a solid backup of that original SD card somewhere safe on your PC!
Actually, there's no reason you can't do it while it IS in your TomTom since a backup using your PC writes nothing to the card. If Home fires up when you connect, just ignore it and use your PC to make a full backup of your unit per these instructions: https://www.tomtomforums.com/t17864-how-backup-contents-your-unit-computer.html
After that, we can take the information from your PC to try to build a nice, new 2GB SD card for you that includes your W.E. map and not touch your original while we're doing it.
Hi
When I put in my original UK RoI card (Locked) into the Card reader it showed it as blank when I tried to open it. Even after doing what was suggested on the site you suggested. So I got nowhere there.
I think I have 'cracked, but dont ask me how. I waited until I had a brand new 2GB SD card. and then played with it using a card reader and the old TomTom file I had on my computer, First I got the device to open on the new card but it said 'No Maps' so I then found the Western Europe file, dragged and dropped it into the SD card (in the card reader) and Hey Presto.
Thank you very much for you patience with an old codger. God Bless Frank