Making alpha eraser brush variation presets of existing paint synthesizer brushes can be used to good effect. These can then be used to erase or paint back in a layers information by degree depending on where you set the blend % in the Paint Fill Apply module in combination with the Alpha Fill module settings.
In the example below I've set Alpha Fill to full on such that the blend slider in Paint Fill Apply is Full Off (transparent / black) ) at 0% and 100% is Full On /white. All the stops in between - the shades of gray required for painting in differing layer opacity.
You can then use these manually or use the further modules in the brush synth to automatically erase canvas/ layer information according to the rules you set for their path application based on target source.