Never believe anyone when they say you can't edit normal or mask textures in anything but Photoshop. You can actually do so in any art program that has layers and layer modes (add and subtract). The steps will differ slightly for other art programs, but the gist remains.
Step 1. Duplicate the original texture three times, and make a solid black layer underneath all three. Step 2. Create layers of solid pure red, green, and blue over each one. Set the colors to multiply / darken.
Step 3. Merge the colors into each layer, and set each layer to add, OR, put each layer in a group and set each group to add. This makes it so you can paint over the texture non-destructively.
I also use an auto-action for this for CSP: https://assets.clip-studio.com/en-us/detail?id=1486733
You can also use this to create a chromatic abberattion effect on images by shifting the color layers around! I've used this method in CSP, Krita, and FireAlpaca without much trouble. This works for any textures where properties are stored per color.
