Can apple know that i installed ios 7 beta if i downgrade to ios 6.1.4?

Please? I had ios 7 beta and reset my iphone to 6.1.4. I'm giving it back to apple because it broke priod to the ios 7 beta. I got it without a developers account.

They won't know if you downgrade down back to iOS 6.

Apple can probably tell. You should register your UDID on a site like http://www.instantudid.com/ to be safe. It's only $5 and they did mine instantly.