I understand why you’ve made the change, but it is very poor UX for a number of reasons.
Consider the following 2 Use Cases: (A) updating a STOP order and (B) updating a pending BUY order to increase price (‘chasing up’).
(A) For some reason (separate issue), STOP orders are often refused with ‘price is too far from the market price’. I do not want to lose my existing ‘out of range’ STOP order if the replacement I want is not within market range. Considering you don’t support trailing stops and have this refusal of distant stop orders, it is not sufficient for me to be able to cancel then re-order, as now my STOP may be much closer than I want it to be (e.g. for a volatile stock).
(B) I place a LIMIT BUY order but it’s not immediately executed and I want to increase the price marginally to ‘chase up’. In a fast moving market I want to ‘always’ have an order on the books, so delete and recreate is too slow. Adding a new (higher price) BUY order means that I risk both my orders getting executed and buying twice as much as I want.
Both of these use cases can be addressed with good UX by enabling front end ‘edit order’, then in the back end (unknown to the user), cancelling the old order and replacing it. This solves (A) since I will only submit the replace if it’s viable, and (B) since I only have 1 order at a time.