2001 corolla le with automatic transmission. has over 200,000 miles on original tranny fliud. is it true to change it now would be detrimental ? no slipping ,etc reported.

You can change it just don't have the tranny flushed.
Just pull the drain plug and empty it. Fill it back up with new fluid.
Drive it for 5 miles or so and drain/fill it again.
I would do it 3 times total just to make sure most of the old fluid is drained.

Good luck.

Personally, I'd drop the pan and replace the filter too, as well as check & clean the magnet of any accumulated particulates. Also see if the differential has it's own reservoir or if it is combined with the tranny...change that too if it is separate.

5 miles is a bit short IMO. I'd run for a 100 or so miles to allow some of the crud to be slowly redissolved into the fluid as it heats up from normal driving. Then just do a drain & refill. For full fluid replacement, drain & refill at least 2x because the torque converter retains about 1/2 the total fluid. Hope this helps!

You can change it just don't have the tranny flushed.
Just pull the drain plug and empty it. Fill it back up with new fluid.
Drive it for 5 miles or so and drain/fill it again.
I would do it 3 times total just to make sure most of the old fluid is drained.

Good luck.

I agree 100%. A car with that mileage I would just do a drain and refill.