He probably would not have approved of some of the behavior we see on the courts today. Things have loosened up quite a bit. The younger players see that on TV and respond to it. It also has changed in college where the team atmosphere has brought out some different behavior by players and fans. Unless it is something minor, like the ball toss, you wait until you have time to work on it.
Mechanical flaws can take two, three or four weeks of practice.
I prefer to keep things simple when a match is in progress. Probably the biggest thing I might do is note an opponent's tendencies and suggest a different approach to my player. Tennis seems like such an individual sport. You see some players with the same skills. Some prefer doubles while others much prefer singles.