It turns out they are, if you’ve got some plain old 8×8 LED matrix displays you want to jazz up a bit. In this case, [upir]’s displays were of the square pixel type, but this trick would work ...

This fully-addressable RGB LED matrix was built by [John Graham-Cummings ... to form his 7×7 matrix with the remaining 49 units. A square of plywood with a grid of holes holds each in place.