ethics question

[Marlow]

I bought an MP3 player and it does not work. Unfortunately I had a 2 month lag-time between when I bought it and when I tried it out, so the 1 month guarantee ran out. I wrote to the company and they are basically unresponsive.

Would it be unethical to do the following:
-buy the same MP3 player
-bring it home and put the broken one in the new one's box (forgot to mention that wife tossed old package)
-bring broken one back with receipt and get my money back

The way I see it, I'm doing nothing wrong aside from circumventing a stupid company policy. The end result is essentially the same as if I returned it to begin with and just got one that worked.