Optional Voucher

If you don't want any entry to be shown in the Profit and Loss Account. Then press Ctrl + L in any place.
It can be done while passing vouchers i.e. receipt, payment, journal, contra, etc. It can be done in any voucher. If you want it to be shown in the Profit and Loss Account then open the entry and press Ctrl + L again.
To change the date press F2.