Can one change a figure or an amount when loading a Bill copied from the Purchase Order?

Welcome to the Community space, @dj-white-telkoms.

Yes, since a Purchase Order (P.O) is a non-posting transaction, once you copy it to a Bill, you can change the amount anytime. 

See this article for more information on how to apply a P.O to an expense, cheque, or bill: Apply a purchase order to a supplier transaction.

Get back to me if you have any other questions by leaving a comment below. I'm more than happy to further assist you. Have a great day!