I don't think it is mandatory...I know I read a thread somewhere stating how to get it done without any transmission changes I just cannot find it again.
Found this while searching for the thread. Snipped from here "http://www.torqhead.com/news.html"
"Using a 24x LS G3 PCM and ignition system with a 1994 or 1995 LT1 4L60E car usually meant you had to go into the transmission and swap out components to convert the 4L60E to 1996+ specs. This often brought added confusion, labor and part cost to the LS PCM conversion for 1994/1995 LT auto vehicles. Worse yet, if you did not change these components correctly (year matching parts) you ran the risk of damaging your 4L60E transmission.
Well the days of having to modify your 94/95 4L60E transmission to use the LS G3 PCM are over!!
Our TH LS G3 PCM is not only plug and play with your existing 94-97 engine harness, making installation effortless and quick, it now controls 1994 and 1995 transmissions. We have added some new tech so that the PCM controls the transmissions just like a 1994 or 1995 transmission are intended to be controlled. Simplifying the installation to save you time and money.
Since the internal parts of your 1994 or 1995 transmission are not changing and the internals parts are "year correct" to work with each other there is no risk of damage. Our PCM simply controls these transmissions the way their electronics expect to be controlled and the hardware of the transmission does what it is supposed to do... get the power to the ground"