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.
Also worth highlighting is that using the newer Teamredminer versions, you should set your overclocks, set your timings, and then run the auto-tuner for the algo you want to mine. Let it do its thing for a while and end up with a perfectly tweaked setup.
My Vega 56's (flashed to 64) are happily chugging XMR @ 2340 h/s each.