Because you applied such work to a copyrighted work without the consent or agreement of the copyright owner, you effectively surrender the rights to those works and they become public access/domain.
Romhacks are a legal mess, everyone agrees. But you're saying that mixing original content with copyrighted work will turn (the original content) public domain. Please, show me WHERE I can read this in the North American Copyright Law.
Roy Lichtenstein's "Look Mickey" was made from a copyrighted image and uses two worldwide famous, trademarked characters without permission of their owners. Is "Look Mickey" public domain? No.
The same to Vanilla Ice's "Ice Ice Baby". This song was released with samples of classic "Under Pressure" song used without authorization. Money was paid later to Queen+Bowie - but was "Ice Ice Baby" public domain? No.Copyright violation won't make anything become public domain. It doesn't make any sense.