I have a sub-room system sorted out but am going through part of it to see if I can fully replace a view_b variable which I set to 1,0,-1,and -2 depending on the specific transition effect I want to have with instead just basing most of that on whether or not view_object[0] is noone or not. Doing that makes it so I don't have to hard code when the view is fixed because I can let Game Maker handle that. I've gotten it to work then with fixed view and pit falling (where the view will then have to move back to a position where Link reappears).
Actually though, I wouldn't really recommend my work since it is not finished fully and is a little "stylized" for Minish Cap; not sure if when Link moves between screens in the Game Boy games if he moves the same amount of distance. To this end I would recommend actually what Xfixium had with this old Link's Awakening project he was doing. It was a solid example of what Mamoruanime described, the loading rooms on the fly. Although it is in Minish Cap style the effects should be equivalent enough.
Although I cannot for the life of me find that file though.