Invoking PSP Signal based on Order Source System

Hi,

Can any one have inputs on the following issue

I have following query:

Currently the PSP Signals reprice all the Order Line Items the moment a Line Item is touched. Is there a way to conditionally invoke them only for Line Items with Changed Quantity.

In this scenario Customer is using Handheld application. So Is it possible to invoke the PSP signals based on the orders created from system? 

Detailed Business Scenario:

========================

1.They are using eConsumer Goods Application 8.1.1.1

2.They have two Clients one is Web clients and Handheld client.

3.There will be two people Presales Representative  and Delivery Representative will be involved during this Order to Cash process.