Speak to the dealer when ordering if they can transfer it.. All is good. if not you’ll have to remove it on retention before you exchange and have the plates made up and then have it put onto the new car.
Either way the fee need’s to be paid to remove the plate. The fee is currently £80.
I had issues with mein due to honda being hacked and having no access to dvla directly, so i had to get a standard plate put on 1st and Mb put it on no issue at all. All was done over the phone to mb, luckily for me the dealer made me up the plates for free to put on. I hazard a guess if you was to get them yourself you’d need to ask mb to send you the current v5 with the new reg on..