By the way, violinists don't necessarily have calluses, even ones who play extensively (though some do; it depends on your body and your playing technique). Violin strings generally aren't as hard on your fingers as guitar strings are. I know you're asking about the Braille half of the equation, but if you want (and it doesn't affect your story otherwise), you can also make your character not have calluses but still be a violinist.

Yeah it messes you up because of the reduced sensitivity over the callus. You could use another finger or \*\*\*gasp\*\*\* use your other hand.

Teacher of braille here. Lots of things can affect sensitivity including calluses, how sweaty or cold your hands are, fake nails, neuropathy, and the freshness of the braille among many other factors. You learn to deal with it. If someone is struggling because of calluses I make sure we go over hand care as far as using a pumice stone or exfoliant on rough patches and moisturizing at night. That alone shouldn't be an excuse for not being able to read braille

can confirm, I'm a guitarist who reads braille. I can read through them, sure.

Are used to play violin and I’m no means an expert, but when I played I would hold down the strings with the tips of my fingers closer to my nails. When I read I use more of the pads of my fingers, and I even have some callusing now that still allows me to read. So it just depends on how severe the callusing is

Yes, I've lost sensitivity for another reason. I just use the other hand.

yes it is for sure possible, though I chose to give up guitar playing because the more I practiced the more calloused my fingers were and I did not want to damage my sensitive fingers, though I am sure there are several blind people who do both.