Yes, at least to a point. One method I've used is to paste a custom mask in, then add a new material Texture in the top right corner of the mask editor. You can then set the blending mode of that second texture (or even a third right below it, if you want) to affect the custom mask you pasted in.
For example, yesterday I pasted in a custom mask that highlighted the edges of my model, added a sand texture, and set that texture to Multiply to rough up the edges of my custom mask.
As for adding more than one custom mask and combining them, that may be possible, but I've never done that myself, so I'll leave that up to other users to weigh in on.
1) Click here to browse to your custom mask (the button isn't shown here for some reason, but there's supposed to be an icon there). You can also just paste your custom mask in.
2) Click here to add a new texture that will affect your custom mask.
3) Control the blending mode of the new texture here.
4) Other options for that texture (brightness, contrast, etc.).
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For example, yesterday I pasted in a custom mask that highlighted the edges of my model, added a sand texture, and set that texture to Multiply to rough up the edges of my custom mask.
As for adding more than one custom mask and combining them, that may be possible, but I've never done that myself, so I'll leave that up to other users to weigh in on.
See below. The steps I do are:
1) Click here to browse to your custom mask (the button isn't shown here for some reason, but there's supposed to be an icon there). You can also just paste your custom mask in.
2) Click here to add a new texture that will affect your custom mask.
3) Control the blending mode of the new texture here.
4) Other options for that texture (brightness, contrast, etc.).