I found a way to lower memory clocks with MSI Afterburner, even when this feature is disabled in AMD driver, so, we need:
...................
Weird.
I usually enable Unofficial overclocking "without PowerPlay" and then I can change clocks up&down.
The problem is - if I stop the miner card clocks are stuck at those set in Afterburner (eg cards not downclocking to 2d clocks)
And if somethinmg goes wrong with saved settings - PC hangs.... one must go to safe mode and disable Afterburner
Didn't work for me, so I wrote what helped in my case.