well that depends on what ur thinking
Modifying order would be considered as 1 order, placing a 2nd with extra qty is like 2 orders.
so ur brokerage and overheads could also change.
bcos if it is a limit order ( which it has to be ) than queue position may not really matter unless ur trading very large qty in some illiquid stuff
if u want to beat an algo, bid the new order at a higher pip ( or lower while shorting )