When submitting a Service Order the only place you can change the Quantity is on top screen before you click Order. Once it is in your cart and beyond, you cannot change the number.

We would like this field to be editable and for order totals to be re-calculated.

For example, if a customer orders 5 Keyboards but later on they decide they only need 4 there is no option to change the quantity in Core. This field is used to calculate order totals so there is potential an incorrect amount could be charged to the customer.