Can you trade a pikachu to yellow from red or blue, if so is it weaker can you evolve it and will it walk with you?
... A traded Pikachu will also not behave like the starter Pikachu, acting as a regular Pokémon instead (even to the point of being able to evolve with a Thunderstone), unless it matches the OT and Trainer ID number of the player.
You can trade it, but will not behave like the starter Pikachu.