The title pretty much says it all...
For example, if you have a mesh with side swept bangs on the right, is there a simple way to flip the hair so that the bangs are on the left, without completely redoing the bangs?

**I'm a noob who's terrible at 3d modeling...
Thanks in advance!

I'm not a good mesher, so there may be an easy way. I don't really know. But I'm sure the specific steps will likely depend upon what software you are using to edit the mesh. I know Wings3D (which doesn't work well with joints) has a "mirror" option which creates a reflection of the mesh about a selected face (like an identical but conjoined twin). Perhaps your program has something similar in which you can make such a reflection (and which you could then remove the original)?

You might could try Cat's Mesh Mirror MilkShape Plugin.