If you copied some of the current skins, made a few minor changes and then added them to the mod I'm sure you could create these units. I could already create the 1st SC rifles from the things already in the game, all we would need is a flag. For the 39th New york, you could take the Mexican general uniform, remove the medals and add a few things and boom, it would look pretty much like the image you provided. As for the Chaleston Zuaves I think they could be made from the items already in the game, however there might be one texture that would need making. You could take the 15th Alabama shirt and change the blue and change it to red. And finally for the 42nd Penn all you would really need to do is copy the union hat texture and add the feather... and then add it to the mod as a new texture. Now I know it is more complicated than that in the whole scheme of things but if the textures are added I can sure make the unit from them, if the coding is done to add units.