No, you cannot change your ID number. It is randomly chosen for you when you create a save file in the game. You have no choice in choosing or changing it.
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Yes, you can. Pokemon HeartGold uses the time from your DS settings. So, change the time on the DS and the time in Pokemon HeartGold will change with it.
Unfortunately, you can't change gears on bikes in HeartGold.
no
Pokémon HeartGold isn't out yet. And anyway you can't change language in a Pokémon game.
I believe you can change your "username," but not your screen name." It's unfortunate.