West Midlands Basketball League

Situation A12 has the ball in his hands to take a bonus free-throw when A9 approaches the table and requests a substitution. He is told he can have his substitution at the next possible opportunity but not immediately because the ball is in the free-throwers hands. A 12 takes an unsuccessful free-throw but the referee whistles and indicates that the free-throw must be retaken

Question May the substitution be effected before the free-throw is retaken?