You can if you own the copyright to the content. I don't know the state of Linux, but this is a reason the FSF (and many other projects) requires people assign their copyright to them when they submit code.

It also helps when you take an offender to court. If I contribute to a project but don't assign copyright, then they cannot take offenders to court if my code was copied illegally. The burden is on me to do so.

Of course, all code released prior to the change still remains on the original license.