Having used PrintMig to move all my printer and associated queues to a new print server a while ago, I needed to repoint all the client printer connections, and also to bear in mind that all the print queues from a number of old servers had been consolidated onto one print server.

It seems that you're trying to do exactly what I did, and this is the code that helped me... (the names have been changed to protect the extremely guilty!)

Code:
$NewPrint = "newprint01"

$objWMI = GetObject("winmgmts:{impersonationlevel=impersonate}!//" + @WKSTA)
$qryPrinters = "select * from win32_printer where servername is not null"
$colPrinters = $objWMI.ExecQuery($qryPrinters)
For Each $objPrinter In $colPrinters
	$Name = $objPrinter.ShareName
	$Server = $objPrinter.ServerName
	$Attr = $objPrinter.Attributes
	;? "\\" + $Server + "\" + $Name + "          	" + $Attr
	If $Server = "\\oldprint01" Or "\\oldprint02" Or "\\oldprint03"
		$x = DelPrinterConnection($Server + "\" + $Name)
		$x = AddPrinterConnection("\\" + $NewPrint + "\" + $Name)
		If $Attr & 4
		;	? $Name + " is the default printer."
			$x = SetDefaultPrinter("\\" + $NewPrint + "\" + $Name)
		Endif
	Endif
Next
$objWMI = 0


I just added this into my login script, and as users logged in their printer settings were reset. Hope this helps!
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Breaker