When I was a kid, I suppose sometime in my early teens, I was interested in music theory, but I couldn’t play piano. One time I asked a lady who played piano at our church to play a piece of sheet music for me so I could hear how it sounded. The music was in the key of A, but she played it in A♭. She didn’t say she was going to change the key, but I could tell from looking at her hands that she had.
I was shocked by the audacity of changing the music to be what you wanted it to be rather than playing what was on the page. I was in band, and there you certainly don’t decide unilaterally that you’re going to play in a different key!
In retrospect what the pianist was doing makes sense. Hymns are very often in the key of A♭. One reason is it’s a comfortable key for SATB singing. Another is that if many hymns are in the same key, that makes it easy to go from one directly into another. If a traditional hymn is not in A♭, it’s probably in a key with flats, like B♭ or D♭. (Contemporary church music is often in keys with sharps because guitarists like open strings, which leads to keys like A or E.)
The pianist wasn’t a great musician, but she was good enough. Picking her key was a coping mechanism that worked well. Unless someone in the congregation has perfect pitch, you can change a song from the key of D to the key of D♭ and nobody will know.
There’s something to be said for clever coping mechanisms, especially if they’re declared, “You asked for A. Is it OK if I give you B?” It’s better than saying “Sorry, I can’t help you.”