Migration from a 400 to 450 is for licensing only. Everything else is a retype. They missed the boat on this one in my opinion. The only times it makes sense to go to a 450 is when your 400 is almost maxed out. Rebuilding 80-90 phones and mailboxes isn't a small undertaking.
I was under the impression that when you did the keycode migration that the old MSC card, or the entire system, had to be shipped back to Nortel. I didn't think there was a MSC card exchange program. The few 400 to 450 migrations I've proposed have been shot down due to the price.
It sure would be nice if there would be a migration utility, even if it was an in house conversion that Nortel offered.