Regarding Tron=Rinzler, and how it seemed like it was maybe tacked on, I'm pretty sure it was there the entire time, it was just understated and easy for many people to miss.
At the start of the movie, when Flynn is showing his kid the action figures, Tron has this little light-up four squares making a "T" shape high on his chest/just under his neck. That's the "Tron" symbol, as established by Tron Legacy, although it's a bit of a "blink and you'll miss it" kind of detail that didn't exist in the previous movie.
When Rinzler appears, he has that symbol on his chest, it's just orange (the color of a Clu-enslaved program), not white (the color of a free program).
And then when Tron is shown "dying" in the flashback, his costume is 100% Rinzler, minus the helmet, and in white, not orange. It's just hard to notice because your brain is hardwired to recognize faces, and you see Bruce Boxleitner so your brain says "That's Tron!". Also, your brain is probably following the easy shorthand of "orange=bad, white=good". If you're not looking at the specific pattern of lights, then you're not going to see that Tron=Rinzler. But if you see the pattern in the lights, then you can see the reveal.
And then, Tron strips a guy of his weapon and kills him with it, and then takes a moment to stare down as his hands as now he's dual-wielding two weapons (which is strange, as the weapons normally disappear when the program dies, but Tron "stole it" somehow). And the only other duel-wielder we've seen has been Rinzler.
And then Tron does an obvious "Rinzler" pose before taking on two guys at once. Tron is 100% Rinzler in this fight scene, he just has white lights and he isn't wearing a helmet.
It's another example of this movie doing "show, don't tell", but it went over people's heads because it didn't tell them clearly enough.
Edit: Oh and, the costumes in Tron Legacy were real physical costumes, not CG effects, so the details like Tron=Rinzler were planned out well in advance, and not something they just tacked on in the editing phase.