A fairly methodical AB test, with expected results ~ Will Changing Vacuum Tubes Change Your Amp's Sound? (Full Test!) https://youtu.be/VaO7MmghoqA
I didn't watch the video but they certainly CAN change the sound. Tube characteristics vary and tubes age and eventually die. I'm old enough to remember when almost every drug store and hardware store had a DIY tube tester and they sold replacement tubes. If your radio or TV quit (or started distorting, etc.) you'd pull all of the tubes out and test them and maybe fix the thing yourself.
Transistors & MOSFETs vary too but they are super stable over time (if not electrically or thermally stressed).
Beyond that, the circuit can be designed to be mostly immune to (normal) variations. That's how solid state devices are designed and IMO that's how tube amplifiers should be designed too. But some "audiophile" amplifiers & guitar amps are intentionally designed to take advantage certain tube characteristics. Guitar amps aren't supposed to be "high fidelity" and I can sort-of understand that with guitar amps but there are probably better (more reliable & stable) ways to get a particular "tube sound".
Yeah, guitar guys know that.
Audiophile OCDs too.