Is it possible, either by scripting, binding to tags or some system tag, to remotely update Tag Group polling rates (Rate and Leased/Driven Rate) via either MQTT (preferred) or the Gateway Network?
Thanks in advance!
No, not at present. Best you can do is manipulate a driving tag.
At some point:
Though I doubt changing the rate at runtime is going to be a very good idea, even then.
I don’t think I agree with it being a bad idea 
Being able to update a SCADA polling engine’s rate is a necessity. If you have hundreds of edge gateways and you want to update field wide polling rates there needs to be a mechanism; that doesn’t involve logging into hundreds of designer sessions.
Even if run time is bad and restarting a gateway is required (seems a bit odd and intense…)