I don't know but I think that there's no right to change your stage. However the way I would suggest going about this would be a move within a school as this is fairly common. As a peripatetic I imagine you're not based in a particular school so perhaps your first move should be to move to a Nursery post in a school for a year or so and then ask to move up from there. I would also imagine a larger school having more scope for such a move and perhaps more chance of a teacher who would love to experience Nursery. You could ask for help developing professionally as in courses etc to keep yourself in the loop with things in different stages which would give you more stuff to sell yourself with.