Technically the INVOKE command will be run using the same userid as you logged on with and with the same rights.
This is much like if you run the Windows command mode from an admin userid. To get full administrative rights you have to right click the shortcut and select 'Run as Administrator'. Now if you started PxPlus with a "Run as Administrator" then anything you spawn will also be running as administrator.
If you want to be sure you are launching a system command in administrator mode try:
INVOKE CONTROL "command"
If PxPlus is not already running in Administrator mode the system will ask before running command. If it is running in administrator mode, the command will simply be executed.