I'm wondering the same thing. My first night is Oct 16 and my bands are past the customize stage today. If my waitlist comes through for that 1 night, will I have to customize new bands for that reservation? As far as the fp+ are concerned, I'm not worried about those. They have stayed on my profile without issue even after I changed the first night once already.
I believe everything is tied to your profile, so even if your reservation changes, it shouldn't be an issue. I'm just not sure how everything will work with the bands since during this "test period" they are sending multiple bands to people. I think in the future it will just be one band that "follows" wherever your reservation is. And who knows maybe even now every band we get will work.