You can always reflow it with a heat gun and some arctic silver heat transfer fluid. If you bricked it. Thats what I did about 6 mths ago and still going strong.
Your over-thinking it. I got YLOD on my first PS3 from normal use way before GT5. My new PS3 has taken way more abuse with this game. I say no one has any control if you get YLOD or not its just too random.
This reminds me of a friend telling me not to play DVDs on my 1st gen PS2 because that's not was it was made to do. Well, it's still my DVD player, and still going strong.
There's nothing involved in reloading the game that will hurt the machine. Reloading a game is the same, though a bit more resource intensive, as loading a race or track. Copying the save file is the same thing GT5 does every time you hit the save button.
Nope, won't hurt it any more than playing games on it.