Paint the wing walk on.
Here is a million dollar suggestion. Paint your wing walk areas on, and color match it to your paint.
Tape the area off that you would like. Prep the surface, in this case I guess it is already painted, so sand it for accept another coat. Paint it with a heavy coat and sprinkle the anti-slip aggregate on evenly. This is a paint additive for use as an anti-skid. Usually it is a silica or I think better a light micronized polymeric low profile aggregate. It is light weight and clear. I suppose could mix with paint and spray it on(?), but I recall my painter applied it manually with a heavy "peppering" over a fresh coat he sprayed on the wing walk area. Than with very low air pressure you can blow the excess off and spread it around. It is not hard to get a nice even spread of the grannular anti-skid. Than you put a final coat or coats of paint over the top of the rough stuff. You may want a few coats on top. Also by sealing it with the top coat of paint you keep the little grains from getting into you shoes, which can transfer to the cockpit or other surfaces. I am no paint expert but pretty sure if you are using a base/clear coat system, you can clear coat over it as well.
Usually you do the wing walk after the plane is painted and trimmed.
You can google anti slip paint additives and find a bunch of product. You will have to do a little research. Mine was painted 8 years ago and forgot what brand anti slip we used. I sold that plane fairly recently, but when I did after 1000 hours (post paint job) it looked as good as new. BTW I was using high end Jet Glow paint, a single stage paint and big bucks. The paint has more to do with the longevity than the anti skid materal. Trust me it looked nice and stayed nice. It makes a nice non-slip surface.
Of course when you paint the anti-slip on, you will need to completely cover and protect the whole plane for overspray, to keep this stuff only on the wing walk area. You can practice and try in on scrap metal.
You will have a nice color matched rough surface, looks good and lasts. Enjoy.
Obviously the more paint you pile on top, the thicker the edge will be and the the more mellow you will likely may the surface. However if too thin and the paint wears off, you loose the anti-skid there. Because you used the planes base color paint it will not look bad; You'll just have a smooth spot in the wing walk area of the same color. Like I said mine looked great 8 years later and did not absorbed dirt or oil. It would get dirty but could wash it off with soap and water.
It will not peal and it does not wear off, at least for me. You can always touch up the paint if needed. Even if it did wear, you have the same color in and below as I said. Decal anti skid patches just don't last as you have seen.
There also commercial all in one anti-skid paints. They come in common colors, black, white, gray and so on, however they will not likely match you paint color. Also you paint them on with a brush or roller! That may be OK for you? Some like the wing walk to stick out or be a different color.
