How to make control on Quantity Issue on Technical Portal.

Problem Description ---------------------------------------------------

Navigation : Technician Portal > Repair Execution TAB > Materials block > Quantity to Issue Field

Here is the scenario :

1. A technician enters the required quantity and saves the page/repair order. (NB. Technician does not have permission to Issue the materials)

2. A store keeper then opens the repair order and finds the Materials and the quantity to issue that was entered by the technician.

3. The store user Issues the Material using the Issue Button.

Now the requirement is that once the technician enters his required quantity and saves the page, the store user will not be able to update the quantity entered by the technician. He can only decrease the quantity but cannot increase it.