In Leuven, Article 424 doesn’t literally provide that playing off-key, but it does state that a musical performance must not give rise to “a disturbance of the public order or peace”. However, local authorities have interpreted this provision to prohibit playing off-key.
Art. 6143bb. State Flower Song Resolved by the House of Representatives, the Senate concurring, That it adopt the Bluebonnet song as the State Flower Song. Acts 1933, 43rd Leg., p. 930, H.C.R. No. 24.