@kkarhan @nixCraft

Actually author of the software can change the licence at any time.
Just that they cannot take back someone copy if he/she already get the software.

Of course with contribiutions from other people, they would have to ask every contributor.

But unfortunetly there were free programs that were developed by single entitiy, or require signing a CLA for making pull requests, that are now nonfree.
Like Aseprite.