I'm currently in college and stuck between a CIS or CS major (the answer to this question will not influence my decision, so answer honestly) but I know I definitely want to have a computer-oriented position. In a position where I'd likely get little to no customer interaction, would long hair be an issue? I have Kurt Cobain-style shoulder-length hair. I wash it at least once a day so the cleanliness part isn't a problem. I'm sure I could also work with it to make it look more professional if need be. Would this be an issue or are CIS/CS positions a little more lenient?
That depends entirely on the industry you will be working in. CS is not a field of it's own in that regard. You will always be working for someone who wants more of their manual labor optimized and replaced by more computers. And that someone will decide what the company as a whole looks like.
If you employer is a bank for example, you can expect to adjust to suit and tie for everyday life, while online shops in the fashion industry are probably the other extreme. Any company will have it's own dress code, you just need to find the one that fits.