Customization For a multiplayer game .

I am doing a multiplayer racing game and i wish to implement customization in the game. I have a very minimal knowledge about multiplayer in unity , so kindly tell me that,

What is the correct procedure to apply customization in a multiplayer game. Such as if we change component of the player prefabs in the server side it is not reflecting in the client sides.

when i customize a car in a client will it be updated to the server automatically and will spawn as the the customized car in all screens ? Or i am supposed to do something manually to achieve it ?