Transform 5-unit to 4-unit

[Dan Tracy]

REI newbie here! Just recently closed on a house that was converted into a 5-plex a while back. It's pretty frickin' old, but that's another story.

One of the units is a pretty bare-bones efficiency unit and I was thinking of knocking down a quick wall to combine it with another unit. This would obviously turn it into a quadplex, which (as I understand) would accomplish a number of things:

-It would be a residential dwelling, so I could refi into a traditional mortgage instead of this commercial loan I'm on now

-my insurance wouldn't be as astronomical; I've ran into tons of problems insuring this place simply because it's technically an "apartment"

-there would be fewer tenants to deal with and fewer headaches

1. Are any of my assumptions incorrect?
2. If/when I make this transition, what do I need to do to get it publicly registered as a quadplex, so I can start enacting all my schemes?