ghib

You can just paint as normal.  No need to paint with the PBR Materials.  So just choose the Brush tool, a colour, the Roughness & Metalness if you have the Gloss Channel on.  Click on the 'X Close' in the PBR Materials tab.
 
The PBR Materials are just a way of creating a Substance that you want to paint onto an object.
 
If you think of it in terms of layers that would actually build up on an object in real life and you build up your own library of Materials then you'll actually be texturing your models faster in the long term.
 
So you would have a metal object that over time would have dust gather in the crevices and Oxidization will occur, the object might be painted and scratch off over time.  This is the clichéd PBR example but it helps to think of this when preparing your Layers, which could look like this:
 
 
Dust, Grime, Oxidation
Paint
Metal (bottom)
 
 
You can and will (of course) use both methods for texturing, typically by blocking out your model with pre-prepared PBR materials, and refining with bespoke details along the way.
 
 
 
sorry if this msg came across as being a bit of a lecture.  
 
 
p.s. You can duplicate a material by right clicking on it. then right clicking on the duplicate and choose the folder (PBR sub tab) that you want it to be in.