US Copyright Law Question

I'm not saying I would or would want to do this, but let's take a pretend scenario. Author creates program. Author is copyright holder of program, sole copyright owner. Owner releases program under GPL3. Owner only likes to use their own cord in the official versions. Owner wishes to release it under some other liscense as well, or move all official versions to another liscense. Can owner do that? We are talking owner, copyright holder, not some third party, which may or may not create diratives of the program and release them using GPL3. Same question, other way around. Just want to know the laws. Thanks!