So you are using opaque photo paper? What about clear laser decal paper?

I am sure this is too late now, but you have to do it that way, typically you use a white-backed decal so there isn’t a clear area. Cut the decal and center it.

I have some pics of the OP’s Process to cut the plastic, scan/fix the plastic and apply the decal on my flash at https://pinside.com/pinball/forum/topic/it-was-supposed-to-be-a-simple-flash-restore/page/4#post-5502307

I don't have any trouble cutting replacement plastics. My issue is that the image looks kind of washed out when I use waterslide decals. Has anyone experimented with using translucent paints or perhaps silkscreen?

Here is a pic of my Flash with a replacement graphic. Its not too bad when the lights are off but when they are on you can see the black is not nearly as black as the original. I was thinking of something like silkscreening or painting the black layer on, then using a decal but the difficulties in lining them up perfectly seems like it would cause a problem.

DSC00540-halfsize (resized).jpg

IMG_5909 (resized).jpg