No no no no no...
He's saying that if your tranny needs a rebuild, then simply doing the Jmod won't help. (Like putting a band aid on a broken arm... or a dead person, for that matter.)
What he is saying is that if you're already rebuilding, then rebuild in the manner that Jerry outlines in the tech articles.
YOU DO NOT NECESSARILY NEED TO REBUILD TO DO THE JMOD, BUT IF YOU'RE TRANNY IS CRAP NOW, THE JMOD WON'T HELP.
I think that's it.