At the very least, I would change the filter. Doing so would require you to drop the pan and replace the fluid that was the pan, which is a safe way to change out 50% of the fluid rather than a flush. You have to remember that "lifetime" doesn't mean the life of the car. It's really the lifetime of the transmission. Will changing out the fluid help extend the transmission life, one would never know since there are so many variables that can cause a transmission to fail...one being clutch pack wear, which would happen whether you change fluid or not.
So, it's really up to you to determine whether it's worth the effort. According to my owner's manual, it states that the fluid should be changed at 100k miles. If BMW deems it "safe" to change it at 100k, I would assume that it is safe to do it earlier as well. Afterall, what's so magical about the 100k mark?