Yes, it’s called “Edit and Continue”, in Tools | Options under Debugging. Note that it’s not compatible with IntelliTrace, so you have to disable that if you’re using it. (Thank you Anton Semenov for that info.)
Edit: If you’re using a really old version (the original VS.Net, as opposed to VS.Net 2005 or later), it was pretty fiddly about this (or didn’t have it, I can’t quite recall; I just remember being frustrated). But if you’re using VS.Net 2005 or later, in my experience, it’s enabled by default and works very well. When execution is paused (and you said you’d hit a breakpoint, so…), you can make quite a variety of changes and the environment will happily compile them and continue. Make sure all of the projects you want to debug are in the solution.