This is actually something I have thought a lot of lately. Not just if T changes, but also what it means to us.
Even if it feels more important to actually have T decibels reduced, I think the most important thing is adaptation and how we perceive it. I realized that by measuring T and being relieved when it is milder kind of gives all the power to T. That is exactly when T controls us: if it is loud, we feel horrible - if it is milder, we are allowed to feel better.
I do believe that tinnitus volume actually changes and not just the feeling of it. For me the easiest way to confirm this is by comparing the volume to surrounding noises. Like if my T is at its absolute mildest, the hum & whir from the fridge will mask it. And when it's at its worst, well - nothing covers it but running water (=shower).
What I do not (want to) believe is that the volume of T defines our well-being and that's the end of it - us measuring whether it allows us to have a nice day. I have felt the strongest when I have had such a good day that even the loud T did not drag me down. And I have felt weak when I am happy because T finally allows me a quieter moment, because then I just fear its comeback. One can't deny it makes life so much easier when T steps a bit aside and gives us quieter ears, but what is more important is to have control over it: to be able to push it back even when it's screaming and adapt to it, since there's no guarantee we'll ever go back to silence. Easier said than done, but important nevertheless, I think.