If it's used by an airline for passenger services it'll need to be maintained by an EASA 145 approved maintenance organisation. There's no reason the RAF couldn't apply for this status though provided it's Engineers are EASA Pt 66 Licenced, this can be achieved fairly quickly for experienced engineers.
I suspect that the RAF won't need to - AirTanker will probably provide that organisation and more than likely employ a proportion of licenced RAF engineers for use on military deployments.