No. "so what your saying is that if you amend the order by decreasing it you still hold the position?," Yes to this.
Let's say you have an order for 500 shares and you are top of the queue. IF you amend that order to 800 shares, the 500 will stay at the top of the queue, where your order has always been and the remaining 300 will be at the end of the queue. ie It is only the extras that get added to the end of the queue.
You can always do a little test away from the market. Put in a tiny $500 order that isn't in danger of getting executed and then when someone comes into the queue behind you, increase the order slightly and you will see how it works.
