If you take Shadow (pimped King Air) as an example, the RAF maintainers start with a quick year away to study and gain their EASA licences. They also require further time away to work on other civilian types to keep their skills on items that they may not have been exposed to with Shadow. Maintenance can also be completed by civilian contractors under their own approvals, with or without assistance of the RAF techies. The usual RAF engineering management chain have no powers or oversight as the buck stops with the licensed RAF technicians who coordinate directly with the various civilian authorities.
The only challenge is keeping hold of these SNCOs once their RoS is completed.