Your DP is being an arse. Whether this is a temporary state of affairs or not, only you can know. I think impending marriages can do strange things to people's views - I am very firmly atheist, and wanted to get married in a registry office. My DH said if he couldn't get married in church, he wouldn't marry me at all
. We eventually got married in church, with me opting to amend my vows, but in the 9 years we have been married, he has probably only been to church about 10 times since. So he made a big deal out of something that isn't a big deal, IYKWIM - honestly, the thought of marriage does funny things to people.
However, I didn't change my name - I had built a career under my surname, and didn't really want to change it to my DH's more common name. It was no big deal, however I have found that I have organically moved towards a combination of names.
My name for: work, bank statements, some credit cards, passport, my friends and family, some utility bills, dentist, electoral roll, car insurance.
DH name for: some other bills, some other credit cards, deeds and mortgage, driving licence, GP, and school calls me Mrs DH.
Whilst I much prefer my own name, and consider that to be who I am, I don't really care what people call me - but I would definitely care if my DH tried to force the issue.
Perhaps your DP doesn't realise that changing your name is just a matter of you informing people if you want to and when you get around to it, it's not like you get a brand new legally binding birth certificate IYKWIM!
Anyhow, I would be inclined to take your Mum's advice. Don't give his silly ideas any oxygen. I'd be muttering things like, 'oh well, that's a shame, can you pass the jam?' Call his bluff, but if you make a big deal about it he will become entrenched.