Every change in DNA is not "evolutionary" in nature. However, when it comes to viruses they're more like loose code ~ like the old JCL IBM kept under continuous development ~ you could use the stuff, or not, to make jobs run. In fact, there were so many pathways to making stuff happen a certain way, the meaning of the word "language" was strained.
It's like this ~ sometimes change is effectuated by putting in a new part ~ like a new carburetor in your '57 Chevy. Sometimes you get a Corvette off the same line.
See the difference?