Dude, don't wet yourself.
It's only a theme. I know millions of people who change their themes.
If microsoft were to sure everybody who changed their theme, I'm pretty sure they wouldn't succeed.
It's because of people with your attitude that people go to linux - you scare them.
"OHMEIGODZ CANT CHANGE ANY WINDOWS STUFF ITS ILLEGAL"
"Really? I'll find an OS that lets me do whatever then."
(well, not that I know, but I'm sure a percentage switch for such a reason)