As i don't have vega gpu's i can't really help you, but if you use "restart_devices_on_startup" with the new "restart_devices_on_startup_script", it should give back full speed to your Vegas, and in the script you can add undervolting overclocking etc with overdriventool.

Or try what @lebuawu2 wrote.
But the disable/enable should be enough tho.

Download V1.5.1 and try it.