WARNING: Improperly changing CRTC or hardware settings can be harmful to the video card and attached monitor. Configuring graphics hardware may be a rewarding process, and many have achieved their goals with success and have even tampered with them well beyond their original specifications. Fact remains that there are several known instances of monitors - CRT and LCD alike - burning out after being fed poor data. Similarly, the video card might lack similar safeguards against accidental misconfiguration.
DISCLAIMER: The information provided might not be accurate, and using it is to be done entirely at your own risk. There have not been any reported mishaps in the entire history of OSDev.org, but in the odd chance you break something, we are not responsible.