Instead of hard-coding the destination path, maybe you could use fnGetSpecialFolder() - Returns the path of a Windows Special Folder to retrieve the Application Data folder and append the rest of the path to it...

Code:

; replace pn.ini on 9x clients
if ingroup("Citrix_pn")
  If @InWin = 2
    $sAppData= fnGetSpecialFolder("AppData") + "\icaclient"
    copy "\\server\netlogon\pn.ini" $sAppData
  endif
endif