After applying the .reg and after rebooting you must go in wattman and click reset. Then click manual voltage settings and then click apply. Next to got HBCC slider. If it's on, turn off, turn on again, slide to the max and apply.
Also note line 3, where I have 0001 is my board number as seen by Windows. Your Windows might have assigned a different number so you have to change it accordingly.
Detailed info and source here
http://www.overclock.net/t/1633446/preliminary-view-of-amd-vega-bios/250#post_26297003quoting hellm
"Your clockrates will be still at stock, as will be the voltages, cause you applied them previously. So, open Wattman, and hit the reset butten; don't close Wattman, you have to change Voltage Control to manual again and then apply.
Done! The voltages and the clockrates you entered in SoftPowerPlay should work now."