I would like to personalize my MBPR... maybe something like: 
My problem is that i would like to change it on a daily basis, like the "Frank" does with hes hats (see 30Rock)... so, a stencil is quite not a optimal solution, because i would be able to use it only once but i could print the image on a magnet, like a fridge magnet, and replace it everyday, my question is: is there a part sensible enough to get damaged by a weak magnet like the one i'm describing?