I've checked Win10 + RX480, it seems it works, I see voltage changes in WattMan if I restart it. ADL does not report any errors.
Just to be clear:
Claymore 9.8, running on Win10 + AMD Blockchain drivers can overclock and underclock all parameters for the RX480?
For now, looks like undervolting works only for RX400 series.
I have 2x 580, 1x480 and 2x 560. For me, undervolting works only for RX480. I'm sure that next claymore version will have a working solution to undervolt via bat file... atm this does not work with blockchain driver.
Everything else works great and the hashrates are great.