@Mirabai said
To alter a knitted collar you need an experienced knitter who can unwind the wool, and reknit with no pattern.
I agree, and I know someone who does things like this. She’s much braver than I am.
On Monday she showed my knitting group a 30” tunic she has been knitting off-and-on since 2016, it’s 680 stitches round on 1mm needles. I’ve never seen fabric like it: it looks woven.
(Edit - I’ve checked her project page, she’s knitting it on gardening wire)
She also knits for others, for a specific charity.
However, I’d go with the many suggestions to wear your dress as it is and I’m sure you will continue to receive compliments on it.