Need a little pointers about Iray material editing for versatile makeup

ttmmttmmttmm

I've dabbled in Octane and really love their object system of modes. 

When I fiddle in Iray shaders, I'm a bit stuck, though. Here is what I'm trying to do:

I'll hand paint the makeup in a dedicated layer in photoshop, then export a 16-bit (256 levels of transparency) PNG file as a tint mask for various kinds of makeup, so I can easily use it on various character textures. I'm not exporting the base diffuse texture, just the makeup, or maybe a few custom liver spots or freckles... that type of thing.

surely, there ought to be a way to load this as a separate diffuse of some kind, hopefully with some operators like transparency level or tint color, right?

in Octane, you can just hook a diffuse mix into the base and get creative. Iray inside DAZ is more limited, I know, but there surely is a way without resorting to LIE, yes?

Thanks.