I have to leave in a few minutes, so sorry for the brief answers.
FYI, look over this (it is actually about QA):
Return to Supplier is a DMR-REJ (reject) transaction, but you define the GL code for that, so, it’s up to you there.
That said, I don’t know how you mean “recorded as scrap.” Who says what scrap is? You mean financially? Then set the GL code to a scrap account or not scrap, as desired. Is it “scrapped” because it is DMR-REJ? Well, then yeah it is what it is.
Rewinding, I was trying to get the gist here. So these are warrantable components of what you sell? Like you sell a pen and they send back the cap as defective? And you buy the cap from some supplier?