YES, you got it. Technically it is possible to change it, but MB has no service interval published for the transmission fluid. I wouldn't consider changing it for several hundred thousand miles (assuming you actually own it that long). BUT if you think the radiator was replaced, that involves removing the transmission cooler lines, and they may have lost some of the fluid because of having the cooler lines removed, so for that reason it may be a good idea to have the transmission fluid level checked, but again it is a complex process to check it.
Gilly