I think Sesshoumaru's hair has given quite a significant role in some fics. Some people may be offended if you cut it down (I got some complaints in reviews when I did that) but you can't really write anything if you're afraid of stepping on other's people's toes. Think of the story your creating. If Sesshoumaru short-haired fits in much better, then do it!
All the power is in your hands, whether the readers like it or not. ;D Just make it plausible and have a good reason for cutting his hair, and they'll be more willing to accept the change.