marcreid,
This is not an MCD with shared extensions so I don't think it will work exactly as you are expecting it to.
When you have two MiVO-250s they are considered to be separate, in terms of devices, and there isn't a failover option.
So, what you would have to do is create the phones on one system until you reach the limit you want and then program the remainder on the other system.
What we have done in the past is logically separate the build(s) into sections that allow for an even amount of phones on each system. Then we would centralize the mailboxes onto one of the systems if they didn't have Voice Processor Networking; which doesn't work as well as you would think.
Anyway, what you are seeing on the phone is what it would get from an MCD or MBG once it comes up on it primary (core) system and then finds out what its secondary system is. The only way for you to change that would be to manually touch each phone and program it for what you want, but you can't have the same extension number on both systems; so again it won't work the way you expect it to.
Sorry,
TE