Im using reshade with ESO otherwise it doesnt work but i wondering, do i need to restart the game if i want to see the effect of a new preset or is going back to the char screen and then goin back into the game enough after loading a new preset witouth breaking anything ?

Press the break key on your keyboard to reload a preset after changing something while the game is still running :) (Applies to games in windowed mode, if you're running fullscreen alt-tabbing should reload the graphics und thus your shader preset anyway.)