To your first question, I believe you can't rent out Chocobo stables before Disc 2 anyway, so you can't breed said Golden Chocobo, because it would make the game extremely easy (especially since Golden Chocobos can go anywhere, you could litreally ride straight to the City of Ancients before the whole Temple hooha.

As to replacing the Highwind with the Tiny Bronco, I'd imagine this would only be possible with the PC version if you were to hack the graphics. Apart from that it's a filthy, stinking lie.