They can take the data, and then they can change the data they have on themselves and then share that, but the fidelity of that data is maintained, because anybody who looks at something that's created with it will simply go back to the original and compare them and say “Why did you change these things?”
There's another thing I've noticed. Frequently I get this question from government officials who are worried that people are going to change the data. I'll be honest with you: when I talk to developers and researchers out there, they're not concerned about changing the data; they're actually really concerned about your data being accurate. When a Google map is incorrect because the information the government gave Google isn't correct, or when you have spending projections and someone makes a typo in a spending projection document, people don't get mad at the government, they get mad at the company that created the application or that offers the service. So they want to make sure that it's as accurate as possible.
I think people are much more worried about government's data being accurate--and I think we should be--than they are about people changing the data and doing something with it, because when they do, we'll still be able to check on them.