This is a general question. Is it possible to change the license of your creation (in this case something like linux) that have been developed by an entire community, not just Linus? Can it be changed?
Yes, the license can be changed (except that you can't take back the license you already granted on older versions).
No, Linus Torvalds can not change the license of Linux on his own.
Provided no exclusive license gas been given, the copyright holder of a work has the full right to decide under which licenses to offer his work to others. The choice of license can change in time and who the license is offered to.
If there are multiple copyright holders, all of them must actively agree to a change in the license. In a project like Linux, with dozen to hundreds of contributors, this makes it effectively impossible to change the license because it takes just one contributor to block a license change.
How is the GPL a non-commercial License? You may sell everything under any open source License - per definition.
But to answer your question: Of course you may change the license of every pice code, where you are either copyright holder or the copyright holder gave you permission to.
To change the license of a community-project, the easy way is to have a "Contributor License Agreement".
That's the way big companies like Google or Microsoft or e.g. Python or Canonical do stuff. Basically you demand full rights over all contributions from every contributor. Result: Yes, license changes are possible without problem.
For more information, Wikipedia is your friend: https://en.wikipedia.org/wiki/Contributor_License_Agreement
Linux requireres no such thing as Contributor License Agreement. So no: Linux may not change the whole Linux license but only the licence of parts he wrote.
One last, but really important thing, some may not be aware:
Open source => always open source (like for ever)
No one can revoke open source licenses of published software. Even if you would change the license of linux - every line published today will still be effective open source (mainly gplv2). Of course you can't force anyone (e.g. kernel.org) to publish the open source code forever. But anyone previously downloaded the code could legally re-upload everything - so the licence change would just affect new linux releases.
Basically this would fork linux. Because there would be still a community to maintain "open source linux" - and no one could stop them. We would just need to renaim "linux" - because that's still a trademark ;).