Im sure if you have overclocked using a bios option then it will be overclocked 10% and will still be under warranty.
reading this article It says "Since people have been Overclocking their beasts (read machines) to get the maximum out of them right form Day 1, Asus soon began shipping its own overclocking app, the Super Hybrid Engine, with every Eee. That lets users boost the speed of most Eee PCs by up to 10% while staying within warranty."
http://www.notebookcheck.net/Newsentry.153+M5ae6bba59b1.0.html
if theres a button in bios to overclock surely if you press it again it will disable it, otherwise you can use the reset to defaults option in the bios.