ZBrushCentral

Modifying or Painting on existing UV Maps

New to Z Brush so I assume this is a very basic question. But I have a model that I’m painting in Z Brush 3.12…Ive exported out the UV no problem…My query is how do I then make adjustments to that UV down the line (for instance I want to add more detail or change a colour) ?
I can open the model and re-import the texture/UV map, but I just dont seem to be able to paint or modify the existing UV once imported.
I know this is probably an easy and basic thing to do but I just cant find any tutorials that explain how to do it effectively (not for V 3.12 anyway).
If anyone could explain the process or direct me to a tute I’d appreciate it.

Subdivide the model to have about as many polys as the texture has pixels. Then convert from texture to polypaint. You can now do any painting you’d like, and even change the UV mapping if you want. When done, just convert from polypaint back to texture again.