My guess is that since you get leadership points for attending Boys State that makes your application better than if you attended SLS.
I don't think giving up SLS for Boys State necessarily helps your application all that much. If you are chosen for SLS, it's for a reason and because you have an excellent preliminary application. You are already a leader/scholar/athlete and also probably a strong candidate for USMA.
Most applicants for SLS already have leadership points and don't "need" to go to Boys State to enhance their application.
OTOH - think twice before you miss an opportunity like SLS. There are many benefits to YOU the candidate to attending SLS. You have an opportunity to get a small taste of West Point, you spend a week there, have a chance to interact with Cadets. This is all about finding out if West Point is right for you.
Application wise, attending SLS can result in an early LOA for you. You will have the opportunity to have your interview there as well as take the CFA. Honestly, taking the CFA and doing well at SLS is huge. Your scores will mean more than if you take it at home.
If you were accepted to SLS and have a conflict then go ahead and call admissions. They may be able to accomadate you. You never know unless you ask.