Place systemd unit changes in separate file

[jonjonw]

Systemd supports overrides for unit files. Since it looks like you're just adding two values, you could just modify the existing unit file with a .d file.

ie, create a file: /etc/systemd/system/[email protected]/user.conf containing:
[Service]
User=openvpn
Group=openvpn

That way you'll get any fixes in the unit file for openvpn automatically included when there is an upgrade.