Can a purchase order be closed without a Good s receive note? Allso can a date be placed on a GRN?

A PO may be closed with zero receipts. A GRN cannot have the date changed (except in original receipt screen by changing transaction date but you really should not receive outside of current period) however you can change the period using GRN adjustment transactions (which by all rights shoudl be locked down to only accounting or another authority). Changing a transaction date outside of the current period shoudl probably be a no no for inventory type receipts and probably for most others. We close our books at a set day of the month, no exceptions.

You can set the receipt date on a GRN by using the Options>Set Receipt Date function, however this will not change the period of the GRN. You cannot change the period on receipts, but you can change the period when you are matching the GRN in AP Invoice Entry, which will back the AP Invoice in to the same period as the GRN. (AP Invoice Posting>Options>Change Period)