How can udevadm be run with root privileges after resuming from suspend?

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I am using Fedora 25. My hard drive gets set to a very low APM level (power saving). I have set up udev rules to adjust the levels for on-battery and plugged-in states using hdparm. This works as expected. Now I would like to trigger them after waking from suspend/hibernate. This works by running udevadm with root privileges from the terminal/command-line, but not from scripts. The command is:

/usr/bin/udevadm trigger --match-subsystem="power_supply"

I tried creating a systemd service as mentioned in this: http://unix.stackexchange.com/questions/99120/trigger-udev-rules-from-systemd

I have tried the solution mentioned in the above, executing the command as /bin/sh -c '/usr/bin/udevadm trigger --match-subsystem="power_supply"', without success. I have also tried the following:-

• Prefixing the ExecStart command line with a +.
• Adding a User=root directive.
• Putting the udevadm trigger command in a separate script and executing that.
• Executing it from a script in /etc/pm/sleep.d/ and /usr/lib64/pm-utils/sleep.d/ instead of using a systemd service.

None of this works. Either the script isn't being run at all, or the udevadm command isn't getting root privileges. How can I run the udevadm trigger command with root privileges from either a systemd service or from a pm-utils script after resuming from suspend?