AC Power Cord -- how not to get Apple Care replacement - is there a written policy?

I had a cord about 8 years ago that was replaced by Apple Care (it no longer charged the old Mac Powerbook).

Well, my power cord a few laptops on (my present MacBook Pro 2011) needed to be replaced (the connection at the end where the cord meets the body appeared worn -- maybe I streched it out or kinked it too much). And so I checked here and googled other forums to see if I could take it into the Genius Bar rather than deal with Apple Care on the phone. It appeared from the discussions here and elsewhere that Powercords were sometimes replaceable, and sometimes not.

The Genius bar refused to replace it. I'm not upset because, as a temporary measure, where the cord was worn, I opened up the insulation to see if I could adjust the wiring to get the to work. Tweaking it did get it to charge for another few days (work deadlines!) until I could get to the Genius Bar. But it's probably because I opened up the insulation that they balked at replacement.

So it goes.

But I do wish Apple Care would've covered it. It's not super expensive but in this crummy economy, every little bit helps.

Maybe it depends upon the luck of the draw: who you get to accept (or reject) the return? Or is this thing warranted only in a "discretionary manner"? Is there a written policy?

I guess I could try to go through Apple Care on the phone, but I'd have to send my old cord back from what I can tell, and then might get charged for the new one?

Anyway: just a recommendation: if you're cord is on the fritz, don't tamper with it to try to get it to work: you might endanger your chances of getting an Apple Care replacement.