According to the archived Energy Efficiency Guide for iOS Apps I should be able to change an NSOperationQueue's qualityOfService and promote its operations to the new qualityOfService.
This does not seem to be true anymore but I can't find any current documentation on how to promote a queued NSOperation.
Does anyone know how to achieve QoS promotion of a queued operation? It seems like whatever the operation's resolved QoS is at the time it is added to the queue is the QoS used when the operation is run regardless of changes made to the queue or the operation before it runs.