So, I have an order that fills partially. When I update that order with a replace_order() call, what does the new order take as quantity?
For example, initial order of 100 shares, of which 50 are filled.

I replace the order with a new limit price, and leave quantity the same. Then, is the new order for the original qty of 100, or for remaining 50?

I replace the order with a limit price and a new quantity, say 80 shares. Then, is the new order for the specified 80 shares, or the remaining 30?