Faiz - Are you talking about HQ or SO for your changes?
Your post mentions POs, and that you would like to modify the Qty and Price (both can be done) however where a PO actually says 'Price' (only in HQ does it do this) it really means system Cost - so, are you looking to update Cost, not Price? If yes - you do not want to use a task 110, but rather a task 130.
Also - you can import a PO in both HQ and SO provided your fields match up, this is going to be one of the easiest options for you.
For sure let me know about the HQ vs SO thing as that will give the responses a good basis.