An EndIf will terminate the If statement but it will not terminate the further execution of the script.
If just one condition should be true and executed then you could use Select - Case - EndSelect like show below. If one Case statement is true then all other Case statements are skipped.
Select
Case InGroup("Print_Lager")
DelPrinterConnection("\\SERVER\HP LaserJet 600 (RESEPSJON)")
DelPrinterConnection("\\SERVER\HP LaserJet 600 M601 (NPID8D2BE) Ny")
DelPrinterConnection("\\SERVER\RICOH MP C4503 (NY)")
DelPrinterConnection("\\SERVER\Xerox WorkCentre 7855 PS")
AddPrinterConnection("\\SERVER\Xerox WorkCentre 7855 PS")
SetDefaultPrinter("\\SERVER\Xerox WorkCentre 7855 PS")
Case InGroup("Print_Admin")
DelPrinterConnection("\\SERVER\RICOH MP C4503 (NY)")
DelPrinterConnection("\\SERVER\RICOH VISMA")
DelPrinterConnection("\\SERVER\HP LaserJet 600 M601 (NPID8D2BE) Ny")
AddPrinterConnection("\\SERVER\RICOH MP C4503 (NY)")
AddPrinterConnection("\\SERVER\RICOH VISMA")
AddPrinterConnection("\\SERVER\HP LaserJet 600 M601 (NPID8D2BE) Ny")
SetDefaultPrinter("\\SERVER\RICOH MP C4503 (NY)")
Case InGroup("Print_Resepsjon")
DelPrinterConnection("\\SERVER\RICOH MP C4503 (NY)")
DelPrinterConnection("\\SERVER\RICOH VISMA")
DelPrinterConnection("\\SERVER\HP LaserJet 600 M601 (NPID8D2BE) Ny")
AddPrinterConnection("\\SERVER\RICOH VISMA")
AddPrinterConnection("\\SERVER\RICOH MP C4503 (NY)")
SetDefaultPrinter("\\SORLIEDC\HP LaserJet 600 (RESEPSJON)")
EndSelect