Sorry just so you are clear and not wanting to confuse the situation - you state "before I am filled", which implies that you have had a part sale.
If this is the case and you have recieved ANY stock into your existing order (as a partial buy)and you amend by increasing the order, you should incur another charge. If you have had no hits into your order, then increase as you like and the additional stock is head to the bottom of the pile.
