I always come back to the aftermarket Off-Road arena with these threads. If this was as big a deal, then the 4x4/off-road industry would be gone.
When my Dad got his Jeep years ago, the first thing that happened was a front cage installed. Welded to the existing factory rollbar. Fabricated at a welding shop. When I got that Jeep years later, I changed to a newer style factory rear rol bar. Then added a different front cage kit that had better head room. Then, when the kid was born, I added a "family cage" to that back.
Everyone I knew that had Jeeps MB/CJ2a/CJ3B/CJ6/CJ5/CJ7, Bronco's, Scouts, Land Cruisers, Blasers, we all did that.
And, If I were to get a Jeep again, it would be the first thing I would do.
So... What is the difference to tractors? Do I now have to worry the rest of my life about the Jeep I sold with the modified ROPS? That's a rollbar.
All of this too, would put race car fabricators ect out of business.
I would not advocate just going out an hacking on a ROPS. On a tractor or a Jeep. But, I do not think it is that huge a deal. I would though, want it welded by someone who really knows how to weld... I would not weld my own Jeep ROPS or tractor ROPS; I know I am not a very good welder.
it' s not about magic.. it's about liability to some extent.. and engineering and materials to another extent.
the person modifying the rops may or may not have a better design than oem, and may or may not have used materials or techniques better than oem.. however.. once he modifies it.. he loses any liability protection.. and in fact I can think of ways he takes on liability himself if another gets hurt using the machine and it boils down to a failure that the oem rops would have survived.
in many things in this world you don't need to worry about the engineers.. you need to worry about the jury....
soundguy