Even further to that, talking to lawyers throughout the clerkship process leads me to believe that many people who held an idea of what area they wanted to work in throughout university and into a professional career still change their minds.
You've indicated you want to work in what is quite a specialised area of the law. If it turns out that you're more interested in an area of the law with any sort of commercial basis, or just in business generally, you might find yourself at a bit of a disadvantage.
In that regard also I would say that to keep in mind too that it's not impossible to move into those fields having done a non-law degree that isn't commercially oriented and vice versa.
Eg I did a business degree but have no intention of going in corporate-related legal fields. And I know of a fair few UWS students who did the criminology social science degree who are now working in corporate areas, including at least one i know of at a top tier firm.
So yes it may be disadvantageous but it won't be the end of the world if you do change your mind.
Also i would add to comments that people have made as far as changing your mind goes - to be perfectly honest, of everyone that comes to mind that I have attended uni with, I am the only person who has stuck with what they wanted to do from the beginning to some extent - and even i have changed slightly as initially i was interested in criminal and family but I have decided on family/care and protection as my future career path.
So i would say that sticking to your guns from day one til the end is more an exception to the rule
But please don't be discouraged by these comments if you truly are passionate about criminal - i mean, we don't know you personaly so perhaps there is something in your background that would place you in the exception category. Just make sure you investigate as many options as you can and don't simply go with your first choice without considering others