Gaining Access to Restricted Cells on Spreadsheet

Hi guys,

I happened to come across a post on purchase order from excelforum.com and I am very delighted to see such a robust and practical PO.

Credit to Norman May for sharing such a good piece of work, however there is a question I would like to ask regarding the "History" sheet.

Is there a way to unrestrict the top most cells of the sheet, where it holds the label for the data? I would like to add/change the title accordingly. I have tried modifying the codes for it but it didn't work, it keeps gving the "The value you entered is not valid, a user has restricted the values that can be entered into this cell"

As attached is the Purchase Order.

Thanks alot in advance,
Faiz