I'm struggling to see how the current workorder line item "warranty" functionality is useful. All it does is mark the item as warranty and set the price to $0.00. Now, this would be workable if it didn't remove inventory and didn't reflect negative profit, but it does. It both removes an item from inventory and deducts the negative profit dollars from our daily profit. I honestly can't even think of a single contrived situation where I'd ever want to push that button. Warranties should never hit your profit...otherwise it's not a warranty.
I'd like to suggest a couple idea. The easiest for my shop is to have any item marked as warranty be set to full retail, not change profit dollars in either direction and not change inventory. For the bike industry, warranties require receipts with serial numbers. Having a proof of purchase for a warrantied item is very important as occasionally we'll have to warranty the warranty. Or the customer will have the bike stolen/damaged and need to report a serial number and retail value to the police or an insurance company(hence needing warrantied items to reflect full retail of the replacement).
There are other solutions that I could also work with, but the current system just appears to have no actual real world uses.