Yes you are, there is a house in Lavender Town with the nicknamer. He will say would you like me to rate you're Pokemon name? It's great. Would you like a better one?
lavender town
You should be able to rename a Pokemon any number of times in the game.
You will NEVER be able
Registeel is not catch able in Pokemon LeafGreen. In order to get a Registeel you will need to trade for one from Pokemon Ruby or Sapphire.
You cannot catch Registeel in Pokemon LeafGreen. This is due to FireRed and LeafGreen being able to trade with Ruby and Sapphire. Pokemon Ruby and Sapphire have the three legendary golem Pokemon including Registeel.
Vulpix is an exclusive pokemon to Leafgreen version if you trade one from Leafgreen to Firered you will be able to have it.
You can rename a pokemon by going to the Name rater
Yes you can trade leafgreen version Pokemon to another leafgreen version.
Defog did not become a move until Generation 6 so you will not be able to find it in LeafGreen
No, you would have to make the code.
Not in Pokemon leafgreen only in Pokemon Firered never ever in Pokemon leafgreen And in Pokemon firered it is rare in power plant not available in Pokemon leafgreen?
Go to Lavender Town, the one with the Pokemon Tower. There should be a house where you can change your Pokemon's name. There should be a sign near the house saying Name-Rater. you go to Lavender Town and look for a house that says Name-Rater