Does science (as you use the term) involve the constant revision of how we talk about or define things to reflect our best understanding of those things at the time?
Yes, that is science.
Is studying this after the fact good science?
Is science (again, as you use the term) taking action in response to an immediate crisis based upon your best understanding of a thing, while still committing yourself to learning as much as you can about that thing moving forward to fill in whatever knowledge gaps you might (or might not) have?
Yes, that is also science.
Is this hoping and dreaming, not yet based on studies, science?
I have no idea what Fauci said, or even what the context was for what he said.
There is a difference between science and opinions. People have opinions. Science is a process. "Hoping and dreaming" is what inspires a person to want to walk on the moon. Science is the process that gets you there. There is also a vast difference between science, and managing a (notoriously ignorant) public's perceptions and reactions to that science.
Boris Johnson is anything but a scientist. A elected politician making policy for his country may, or may not, have anything at all to do with science. It's certainly not an action that can be equated to the scientific process itself.
Science didn't happen prior to 1964, correct?
Incorrect, obviously.
As science itself has progressed, not to mention relevant things like technology, the scientific process has also progressed.
People were using genetics principles (like selective planting) for agriculture long before we even understood what a gene was. Our knowledge of genes, and subsequent ability to document, discuss, and manipulate them, has revolutionized the field to an indescribable degree since then, to the point where comparing the two different times is laughable...but that doesn't completely invalidate everything that came before, or make it less than what it was for its time.