When we lived in Michigan I used the exemption form for my son for preschool. I didn't claim religious though, Michigan has philosophical exemption as well. I actually don't remember putting anything in the reason spot, and I believe I had read that the less info the better, so I probably just wrote that we were philosophically opposed to the practice of immunization or something like that. I had no problem with the school, but it was the preschool at the public elementary and they had received waivers before.
We are in TX now and I've submitted an exemption to the public school for DS#1 and now one for a private preschool for DS#2 with no problem. I think that we think worst case scenario is going to happen and I bet most of the time exemptions are received with no issue.
Good luck, just be matter of fact about it, and if you have a problem, I'm sure someone here will know what to do