Is it possible to send a message directly to a Subscription queue?
Scenario:
A message failed, dropped onto the deadletter, the message has been picked up manual
this is a similar question to the one you asked earlier: Azure Service Bus Subscriber Deadletter
this is not possible, as far as I know. the only thing you could do is to add an extra filter on every subscription that has something like SubscriptionName='SubscriptionA'. If you then want to send you deadlettered message to the specific subscription, you can add a property SubscriptionName to it, to achieve your goal. Take into account that you also have to make sure that in your original filter, you add a condition to indicate that the property SubscriptionName should not exist.
I agree however, that it would be a nice scenario to 'undeadletter' a message, so that it ends up again in his original subscription.