Setting up a freelancing business is as it is a tough job and it may take years to establish yourself as a freelancer in a particular niche. Naturally it may give you jitters if you have to change your niche. But sometimes there are unavoidable circumstances and unless you change your freelancing niche there is less chance of survival. Sometimes it makes sense to leave the sinking boat and start swimming instead (not a good analogy, I know, but what the heck).
Whenever you are planning to change your freelancing niche just make sure you are not hard pressed for money when you do that because, as you may already be aware of that, it may take you a few months and even a year to reach the level of income that you might be earning right now. Whenever you start working in a new niche you have to create a presence for yourself. It may involve redesigning your website or creating a website from scratch. You will also need to target a new set of clients and customers and reorient the way you have been communicating through your social networking profiles including Facebook, Twitter and LinkedIn.
Here is a nice blog post on how to change your freelancing niche and be successful at that.