Our application needs to send “Replay to Queue” name in the MQ connector header along with other header information in the request. There is no such that option available in the request header. In fact Pega 7.2.1 the InvokeMQConnector activity set " reqMsg.replyToQueueName = qNameResponse;" which can be true in all scenarios (see attachment).
Pega should give the option in the MQ connector's request header to select reply to queue like in response tab.
The Out-of-the-box / template invokeMQConnector activity, sets the "Reply to Queue" and "Reply to Queue Manager" based on the values configured / set on the "Connect MQ" rule form under the "Response" section.
See attached screenshot.
If you want to customize / override this logic to read the QM and Q from a custom header you can do that too.