And some images about the shoulder pad stripe painting:

Masking and painting the inside of the stripes:

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Then I widened the outside of the stripes, and painted back with background color the excess. Look from side (e.g. nova logo on image #3 above, I have to fix the borders) to find any irregularities. Even though you can paint only .2 mm wide lines with the brush, you can always narrow it with background color. You can always take a photo and use helper lines in an editor to find where do you need to fix the lines. It can take time, but should be quite a mechanical process.
And I can fail, too, see genestealer magus above.