The transmission can be serviced like any other transmission. The difference is instead of a dipstick you'll have a fill plug on the side of the transmission and a level check process that is different, it uses a level check tube in the trans pan that basically lowers the fluid level when the volume at prescribed temperature is over the tube level. Eric the car guy on youtube goes through the procedure on a V8, which has the exhaust y pipe being removed to get the pan off and change the filter. Yes, not changing the fluid could shorten the lifespan of the transmission and all the other issues that go with that, hard shifts, shudder, ect.
At 121,000 miles, you could go the extra remove the pan and change the filter too, you could do the flush without changing the filter, or you could do a simple drain and fill. I also added the Lucas transmission fluid conditioner.