I was reading about XH558's final years and the captain was flying her as his secondary duty, having previously been a Vulcan QFI before moving over to the Victor.
The Vulcan Display Flight was an enclave within 55 Sqn. Nearly all of the VDF crew were current Victor crew.
So, is that a secondary duty?
It was IIRC. The extra work to stay current on an additional type and the time given up to display warranted it.