coding L4G for sage x3

I am looking for a talented programmer to code a L4G for Sage X3. we have a system for selling items, and we wanted to make a replacement function, which means that we have an order containing several items. if we wanted to modify an item, we sell it off (deactivate it), and replace it with another item, and there are discounts and gotta that apply to the order. based on quantity: for example, if the total number of items in the order is 40 or more, we apply a 20% discount. the replace function I wanted when we replace the item, I wanted that the quantity of new item will not be added to the total quantity of the order. will be calculated by itself. I have the code remains just to modify on the part of the replacement all that it is handed and ... it's already done