You should never add users directly. Have you not heard of the UGLY principle?
Users
Global
Local
Y - cuz it's ugly

Put the computer names in an array and loop through it. You could use ADSI or the cusrmgr.exe utility.
Code:

For each $comp in $comps
Shell 'cusrmgr.exe -m \\'+$comp+' -alg administrators -u domain\global_group'
next



Of course this is simplified as there is no ping check to see if the comps are reachable and success is not logged.
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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.