Ehhhhh...sorta.
It works like this. Tranny fluid is a detergent. It works that way to keep the system clean. For this thread, we are only covering the detergent portion of the fluid. Once it gets dirty, it loses the ability to maintain its other properties as do all other fluids in the vehicle. What happens when you continue to run the tranny with older fluid is that it starts to leave deposits in places where clutch/rubber material used to be. What does that mean? If you replace your burned up fluid with new detergent, it cleans out the old stuff that is now being used as part of the function of either a friction or a seal.
So, if it has gone more than 70K on old fluid, leave it alone. If it is under that, its iffy. If it is between 30 and 50, you SHOULD be okay for the change.
SWS