Yes, as discussed, I have used TCUs loaded with the original software and the upgrade, in my 4200. To start with I had the original software, and I didn't know whether to upgrade or not. Emblem told me that the upgrade was not reversible and I may not like it. So Maverick loaned me his TCU and I fitted it in my 4200 and had Emblem load the clutch readings etc. I must admit now that when I drove the car following this, I didn't pay enough attention to the differences. Anyway, I plumped for the upgrade.
Then, after driving the car and having numerous PIS adjustments at Emblem (sorry Myles), I concluded I didn't like it, and yearned for the original again. Note that my car was a 2002/03 model. For me, the gear change was too slow and gentle, and pulling away fast from standstill was difficult (the car would start rolling, there would be a lull, and then a rush). The original software had it's own issues when pulling away (it was easy to kangaroo) but the changes were much more satisfying (I'd even describe them as brutal when flooring it).
So I set about trying to find a secondhand TCU with the original software again. In many cases what I purchased off Ebay was unknown in terms of software version (you can't rely on the labels to tell you), but eventually I found one. I installed it, had Emblem set the parameters again, and I was off - fantastic. Thumping gear changes, downshift blips, park assist, kangaroo starts, were all back.
On the point about the downshift blip - I had Larini back boxes and sports cats on my car, so the blips were obvious. They may not be so obvious on a car with standard exhaust components.
I had the 4200 for just over 4 years and when it was time to sell, I popped the upgraded TCU back in and let Maverick have the one with the original software which he is still running.
Dave