There are some men who would like a woman with a bald head. Some wouldn't. It is all personal preference.
Everyone is right about you telling the guy about it first. Think about how you would feel if a guy had a picture up of himself from right out of college and when you meet up he is 65, bald, badly overweight, and hadn't showered since the picture was taken? It is all about being upfront with others.
You don't have to make too big of a deal about it either. Just shoot him a message and say something like, "Hey, just wanted to let you know that I did something impulsive the other day and I didn't want you to be too shocked. My appearance has changed since I had that picture taken. My hair is a lot shorter now (like non-existent) and I have a nose ring. No biggie, hair grows back and all, but I wanted to give you a heads up." Or, change the picture on your profile to a brand new one and shoot him a message saying, "Just so you know, I did something impulsive to my appearance the other day and have posted a new pic on my profile. Let me know what you think."
If he shuts down the date because of that information, then it tells you something about him and saves you from some unnecessary drama. Not even the appearance of your bald head, but the fact that he can't handle impulsive behavior llike you are prone to would be an issue.
Good luck.