Fixing slight cosmetic issues with Photoshops Layer Masks - instead of creating a mask in Pixinsight

As always, I tried to remove the magenta from my latest narrowband images. And while it worked well on all the stars it also left some cosmetic issues in some bright areas of the image:

I tried a couple of adjustments

• adjusted the formula to adjust green - but either the stars stayed magenta, or I created these artifacts again
• used an inverted star mask to protect everything but the stars - but because the magenta color is mostly in the fainter outer halos of the stars, it didn't work
• used a range mask that just selected the areas where these issues occurred - but I could adjust the mask fine enough

I ended up fixing it with a completely different idea from how we blended the milky way images:

1. I stored the image before running Pixelmath to remove the magenta and after.
2. I open both images in Photoshop as layers with the processed image on top
3. I create a "Reveal All" layer mask on the top layer
4. Carefully drawing with black brush over the areas with the cosmetic issues - thus revealing the unprocessed image underneath

And now I could load it again in Pixinsight for final processing.