There is a name rater in Castelia city.
You can rename a pokemon by going to the Name rater
You should be able to rename a Pokemon any number of times in the game.
You'll find the name rater at Castelia City. It's the building north of Central Plaza on the left.
There is a name rater in Castelia city. In a building just go on the street diectly east of the Pokemon center
Go find cecilia and click on change poke'mon name and change it. only on REPEREDS^ mode.
In slateport city there is a name rater who can rename your Pokemon remember Pokemon traded to you can't be renamed.
You can rename pokemon when you first obtain them or ask the Name Rater to change it. The Name Rater is in Lavendar Town he's in a house below the Pokemon Center. Bring the pokemon you want to rename to the Name Rater then he will let you rename it. Keep in mind pokemon obtained through trade cannot be renamed.
In Eterna city where the second (grass type) gym is, go into the apartment block and on one of the floors there is an old man who will rename your Pokemon. He will not rename Pokemon that you got in a trade though.
No, you can't rename traded Pokémon legitimately, you will have to use a cheating device for it such as an Action Replay. Here is the Action Replay code for it. 5215BE54 2800FB2B 0215BE58 B0022001 0215BE5C 1C388028 D0000000 00000000
The Name Rater will rename any of YOUR Pokemon. If you own a Pokemon that originally belonged to someone else (Like the Machop you trade for in Goldenrod), then he wont rename it.
Black Kyurem is in Pokemon Black 2.