I’d do three things in your situation.
1, Get on the internet and find the official spec’ for both cars and compare them. The old one will be out there somewhere.
2, Ring the dealer back and ask him straight up if ANYTHING is different apart from the name.
3, Ring Mercedes UK customer service and ask them the same question.
It sounds like they just want you to sign an amended order form, which is fine. You’re not required to provide your PIN until delivery day and you have inspected the car and are completely happy that it is what you ordered.
If I seem a little strange, that's because I am.
Skoda Karoq SEL.