save and load renderer data on a unit composed prefab

Hi everyone :)

I have a level editor where my player can modify a choosen prefab by drawing on a grid (actualy with OnMouseDown). This prefab is made of mutliple unit element. (the grid is 11x11) There's only one type of unit element and it have two states: renderer.enable/disable.

When the player go out / go back to the level editor. I want to be able to save and load the prefab with its units states given by the player.

Should i use XML or txt file ? Should i draw the prefab when starting level editor ? Actualy i only have to store the enable/disable data since the grid will allways be filled with my unit element. Beside i'll sometime have to give to one prefab multiple tags (not necessarily "unity tag"). Not sure of the method to apply, any advice are welcome :)