discount manually for specified customer

hi friends

we have an issue as below :

in orders for a specific customer and specific price list , we want to set discount manually . for example  the item`s price in price list is 35800 , we want to allow user to change it into lower price like "34800" for specific customer.

after that we want to view adjustment for this line and see that adjusted amount is 1000, also at the end in invoice we should have 2 line in invoice, one is the sales price and one is the discount , now we implemented by defining a qualifier which set the customer and price list conditions, after that we defined a modifier and used "