A lot of casio have LCD, the structure is kinda like this from what i've seen
View attachment 32995
So I take out the difuser and scrape off the reflective sticker. The numbers is kinda floating, so you also can do a transparent mod or something like that. But I replaced the sticker with a 2x1 cm printed image of an anime girl, then you get some thing like that.
It's kinda easy, you just need a screwdriver, something to scrape off the sticker (I used a box cutter), and 2 steady hands
View attachment 32998
A themed mod with custom straps would be really cool