I had my private plate on my scheme car and removed it before I got my new car (off the scheme) I already had the orginal plates to put on it, as they had a problem putting it on at the beginning of the lease, long story.
I sent the dealer a scan of the V778 retention document/ in your case the v750 and then took the original on the day of collection and I got the new car with my private plate on.
What I didn’t do was contact dwp soon enough to get my road tax exemption certificate and they didn’t send it out after i first contacted them and had to wait to see if it came but it didn’t so they sent out another. So I had to pay for a full years road tax and then goto the P.O to have the class changed when cert came and got refunded the full 11 months left. So If you have that certificate the dealer can also tax it a disabled.