I’ve called numerous times and no answer. If I wanted to add someone to my application would it set me back?

So what if their back ground and everything comes back really good and we don’t mind if the rent increases some?

Where as the apartments are income based, not only would that person you add to your application have to verify their income, they would also have to be approved. There is a good chance it would increase your rent, amd possibly even disqualify you from being able to move in.