If, however, it is accepted that a LAPL, Is both a licence and, by default, an 'SSEA' Class rating combined, then renewing/revalidating the Licence privileges, would be, by the same logic, renewing/revalidating the 'Rating'.
Unfortunately that is not even hinted at in Part-FCL.
A CRI could however, carry out 'Differences Training', as this does not renew/revalidate a rating.
As it is an 'Appropriate' Instructor Rating, I believe that a CRI may carry out any Dual Class Training, including 'Differences Training', they like.
Any such Training could be used towards
Class Rating issue, revalidation or renewal because that is stated in the CRI privileges but, the conundrum is, can it 'legally' be used to extend an LAPL Holder's
Licence privileges?
Differences Training is signed up in a student's Log Book so any problems, if there are any, would only likely come to light well in to the future. Which is why I would rather it was officially confirmed (Yes or No) now.