This is so true, and expands wildly beyond the area of mastery. I was in the fortunate position to be able to spend days with numerous world class piano masters, both during rehearsals, dinner & regular daily activities and was always impressed with their "breaking of rules" both on and off stage. Some do this completely natural (Lazar Berman, who picked his performance piano within one minute "You have to understand, picking out a piano is like picking out a partner, you feel within seconds if you like her or not." ) with others it felt more like an act (not going to write her name, but she insisted to have a friend turn the sheet music, who was not able to read music and thus was either too slow or fast and she had to swiftly flip to the correct pages while performing...).
The more mechanical piano players where never really my thing. I love the players with their own style and interpretations & personal particularities (Lazar Berman again: Bring me to some cheap shops, I get tired of all the fancy places people take me all the time."). Critics are often not so much into that, however. So the number of "rule breakers" was always limited to a maximum of something like 20%.