Getting unit configuration from /etc file

[shiva@xxxxxxxxxxxxxxx (Kenneth Porter)]

Is there some way to fetch a unit variable's value from another file in 
/etc, instead of having it hard-coded in the unit file?

I'd like to use IOSchedulingClass in a unit file, but I'd like to fetch the 
value (idle or none) from a file in the service's /etc directory, so the 
admin doesn't have to copy and edit the unit file from /usr/lib to /etc. 
That way upstream updates to the unit file won't have to be checked for and 
migrated into a custom unit file in /etc. The local setting will 
automatically be applied to any updated unit file.