There isn’t an ethical issue if you commit based on a FA pre-read that turns out to be inaccurate as in scenario 1. However, I can’t really see that happening. I don’t have experience with NCP waivers but I would think the FA office won’t generate a FA pre-read until making a decision on that. I’d expect clarity before committing.
As far as committing based on a FA pre-read that is accurate, then later deciding to go someplace else because it ends up being a better financial offer, I’d say that isn’t a great way to approach things. To me, the coach and school are acting in good faith and if you commit you’re agreeing to attend based on the terms they present. If you’re not sure then maybe it’s not the right fit.
Obviously make sure to follow the explicit rules, as I’m sure you’re planning to do already. But whether or not some version of the latter scenario is acceptable is probably a judgment call. I’ve seen kids make changes for good reasons that others might question.