If the bearings were that fragile, tonearms would wear out after a year or two of regular use. In most cases, they are not. I am more worried about the snowstorm we are now having. Obviously, this assumes you take normal precautions not to apply too much rotational torque to the bearings whilst tightening the headshell screws. Since the screws that hold the cartridge to the headshell rotate in the horizontal plane, if you just immobilize the arm wand while tightening them, I cannot imagine doing any harm.
tonearm bearings. How do we attach cartridge without ruining bearings?
I have always taken the tonearm or headshell off of table to tighten cartridges. When a cartridge is tightened isn't there a possibility of ruining the bearing in the tonearm if the arm is not removed to allow tightening of cartridge fasteners?