In Japan, tons of school kids do things to their uniform.
I go to a university right now, with no uniforms, but I used to shorten my skirts, tie the ribbon on my uniform much shorter than what the school tells you to, and so forth.
There were a certain type of leg-warmer esque socks that were popular at the time, but our school forbade those socks, so us girls would wear those socks straight, instead of slouched. Then, after school, we would scrunch them down like leg warmers.
Other things I did against the school rules were:
I got my ears pierced (Universities allow piercings, not other schools).
I had long nails (long nails were prohibited).
I painted my toenails (technically, you weren't supposed to do that either, even though teachers couldn't see your toenails).
I occasionally wore clear nail varnish on my nails, and a little bit of makeup. (Japanese high schools and under forbid any kind of makeup.)
This was not a independent school; just an average school.