Update

Just added a 4 sided modular tissue box profile that allows for swappable face plates on each side of the box. 

This is a modular tissue box cover that designed to go over standard 4x5 Kleenex tissue boxes. Its got a removable face that can be swapped in with new designs.

The face plate is held on by these 3mm x 6mm magnets. You'll need 4 for the box, then 4 for each plate you want to make. You'll want to put a drop of super glue in each hole before the magnets, to ensure they don't pull out.
Here's the magnets I'm using

https://www.amazon.com/gp/product/B096LZNZTQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

I've uploaded the following character plate designs. Also to make things easier I've colored and added them all to the same project file (along with the tissue box itself)

the characters are
Hello Kitty, Badtz-Maru, Keroppi, Kiki, Kuromi, Lala, My Melody, Pochacco, Spottie Dottie, Tuxedo Sam, and the Twin stars

Print instructions

The tissue box comes with it's own built in mouse ears to help prevent warping on the corners. Arrange the box so the top is facing down on the bed, no additional supports needed (and the ears tear off super easy after printing).

The plates also need no supports but they are set with a 20 mm brim as a default. They peal off quite easy and just need a little cleanup with a deburring tool. (i was dealing with some filament that was pealing off the bed so this helped with that, if you don't have that issue feel free to turn off the brim)

I'd be open to including additional characters, if there's a particular request just add it in the comments.

Happy Printing!