How to change a mask into an overlay?

I have gotten permission from a creator to convert some of their files for personal use. The issue I am having is that their original content is more of a mask with specific swatches. I use custom skin tones as well as skin overlays. I don’t have a problem with their content showing up, but the issue is that I can’t get it to match my custom skin tones. I would like to change the content over to work with all skin tones but still have the detail of the original content. I have tried following the create a skin detail for beginners tutorial as well as the in detail tutorial talking about composition method. When I alter the transparency of the content itself and load it up with a composition method of 0, it looks too white and loses the detail of the original content. When I change the composition method to 3 (despite changing transparency), it goes completely transparent.