Important: The setting MUST be applied before mining starts or the value won't change. Even if I closed the miner and tried to apply the setting, it would not take. However, applying via .bat after reboot before the miner started worked great.
This is not true. I change REF on my RX 580 cards during mining and it applyies and changing the mining speed.
I actually had someone else tell me they could change the setting while mining too. For whatever reason (something with the drivers I assume), I could only change it before the miner started. I just thought I'd mention it for those that were seeing the same thing as me.
EDIT: I Just saw your edit, so it appears you can change on the fly with newer drivers, but might not work with older drivers.