My computer is in the middle of a long render, and all the nodes for skin materials are a bit daunting anyways.

To undo changes made with EZskin2, can I simply re-apply the character's MAT?

Yes and no. EZSkin uses the alternate diffuse node while simpler texture sets are usually plugged into the main diffuse node.

Which EZSkin disables by setting it to black and to 0%.

So reapply the original MAT file and if the skin renders black, use Scenefixer to set the diffuse channel to white and 100% again.

Awesome, thanks, I would have never had found that!

If you re-apply a texture over EZskin that doesn't have SSS then the black-skin issue doesn't occur.

From that point on you can re-apply EZSkin over any other skin map.