@cv08 i know you are anxious, but as @MYOS1634 said, the requirement to list a secondary campus has been there quite a while. My oldest applied 8 years ago and she was required.
As for weightings, admissions understand HS profiles. They have LOTS of experience with each different HS and knows the competitiveness. I will never forget 20 years ago when we were debating a new house. I asked a friend (college admissions counselor) if top 20% at {uber-competitive public HS} or top 10% at {middle-competitive public HS} and was told “every college admissions counselor knows {uber-competitive public HS}”. So this can work in your favor if you are from one of those schools.
@anxiousmom711 pointed out, every school has a different profile and admissions understands that.
Good luck all. We are still a little way away from admissions decisions rolling out, but in this case, later might be better. Kids who have been sent to alternative campuses (or directly applied to alternative campuses), will hear first. They actually may start in October. So when a kid announces to friends that he got into UP in October, don’t necessarily believe it. In the past, the earliest I’ve seen decisions roll out is usually early November. Obviously, the process can change from year to year, but that has been the historical trend.
Good luck all!