Can the author of the software (or, more generally, the copyright owner) change the license under which the software is distributed?

Question

Law in IT

Can the author of the software (or, more generally, the copyright owner) change the license under which the software is distributed. More precisely, re-release this software under a different license (perhaps incompatible with the old one). I'm interested in the general case, as well as specifically the following:
(1) Replacing the GPL with a commercial license (with closed source and other pranks). For example, I release a library under the GPL and want to use it in my own commercial project. That is, the new license is tougher than the old one.
(2) Replacing BSD with CC0 (public domain). For example, I have a good impulse to release my BSD-licensed library into the public domain. That is, the new license is softer than the old one.

Answer 1

Yes it is possible. Many libraries are released under multiple licenses at the same time.
As for the replacement - it seems to me that those who managed to download the old version with the old license can successfully continue to use it (and share if it is allowed by the license).