Whatever the strict rules, if an existing member changes roles then would have thought it's largely up to the employer to interpret them at least in their finer detail and to ensure that the employee involved is forewarned of any possible implications of the role change on their pension scheme membership
It sounds like you have someone who has changed role quite dramatically, if it involves stopping (or starting) teaching work. I would start with the role itself - if you were offering it externally, would it have been a support role or a teaching role - if the former, you need to be consistent. If they have a very small amount of teaching in their role, I have in the past agreed to split out a contract into two part time contracts - one a teaching role and one a support role.
