As a teaching Pro you will hear this all the time from your students, "I cannot change this shot or technique because I have a very important match or tournament this week." Or, "when I get under pressure I resort to my old habits or old ways."
The biggest reason most people take lessons is to make a change. A few people will take a lesson to maintain fitness or have a work-out. Most of my students never lose a match because they are not fit; it is because they lack good technique or lack proper strategies. Most pros get in shape to play tennis, not play tennis to get in shape.
You have probably heard it takes about 7 years to get good in any sport. So, you know it will take a little time to make necessary small improvements in your game. When you are actually under pressure in a match and you can muster the fortitude to stick with what you are changing in your game, your success curve will go up dramatically. Sometimes, just maintaining a game is not good enough, especially if you are surrounded by younger more aggressive players. You know, "Life is in the details."
If you are paying good money to a Pro and you trust him/her, then go out and practice in a match what you are doing in the lessons.
Remember, do not even mention the fact that you are taking lessons or changing some parts of your game to your opponents or partner. It will sound like an excuse, "Just do it" as the Nike advertisement says.
Down the road you will be very happy and proud of yourself for making those changes.
Good luck on the courts!