I shape pink foam 3 ways:
1) If I need a clean cut, I slit it with a razor blade or utility knife, going as deeply as possible, and then snap it apart. You can then sand the remaining rough edge to make it perfectly smooth.
2) If I need a rough texture, I carve it with a Dremel tool, using various bits for different effects.
3) If I need detailed textures, such as cut stone or concrete expansion joints, I simply emboss it, using an old set of manicure tools.
