MQTT retain flag set to true?

I have recently started to publish messages using MQTT on the Rio. I have noticed on the subscriber nodes that while the messages are being relayed fine, the retain flag is set to false. Reading through some online info, it would be ideal if this flag were set to true. Is this possible on the Rio or EPIC when they are publishing messages via MQTT?

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There be dangerous waters ahead…

Retain sounds good on the surface, but you really need to take a pause here… Retain means retain. Usually for pretty much ever. So if you make any change to any topic path, you have the new one and the old one. Do that a few times and you pretty much have something very close to a memory leak of sorts.
Your broker just becomes more and more bloated with retained topics.
Depending on the broker, it can vary how it might (or might not) be possible to flush those old retained topic paths.
So that is the cost. The benefit is just that when a new client subscribes to that topic they get the last stale value vs waiting for a fresh value when it is published.

Bottom line. Node-RED MQTT node has it as an option, at this time, EPIC and RIO don’t.