Is there a way (without 3rd party apps) to cancel a specific purchase order line? 

Here is the situation: 

Assume we have a purchase order with two lines. We receive part/all of line 1 and create a backorder for Line 2. We later find out that we need to make a change to the item in Line 2 because that product will no longer be coming, or it will not be needed.

There is a delete button with each line. However, it won't let me delete Line 2 because it is in a State "Purchase Order". On the Purchase Order Line model there is a Status (State) field but I am not able to remove it's Read Only attribute via Studio, probably for obvious reasons. In looking up the field on the actual model, it appears to be a related field to the Status (State) of the Purchase Order itself. No doubt this is helpful when processing Purchase Orders (ie confirming it once automatically confirms each line). However, cancelling the entire Purchase Order is certainly not an possible given the valid activity taken place on Line 1. 

I can add a 3rd line to the confirmed Purchase Order without an issue but I can't even delete/cancel that newly created line 3 (even if I cancel it's related receipt).

It appears that the ONLY option is to change the line's quantity of the product to Zero (and cancel it's backorder receipt). This indeed helps the issue, but it doesn't seem to be a good workflow/solution to me for a number or reasons.

It would seem like there should be a way to change the status of an individual line when it has not had any activity so that it can at least be cancelled, if not deleted. I have not been able to find this and do not want to resort to code/customization/3rd party apps. Can someone provide an explanation why it is this way? Is there a way around this?