For the religion trait, I had a quick look through the traits and triggers file last night.

The three religion trait only have one level and they do not have a no going back level set so in theory you should be able to move from one religion to another, but the only trigger I could find that effected the specific religion of a character where in the creation triggers (e.g. Birth, Adoption and Marrage triggers)...

Which means that there does not appear to be a way of changing a characters religion once it has been set...