After removing the numbers with a sharp knife and a pair of tweezers the result looks promising. A nice sharp edge between the gray paint and the white acrylic. Time to put this test piece along side a printed front on the lightbox and compare them.
The difference is evident. The spray paint method has won. Now I will have to see how many layers of paint will have to be sprayed on. This is in fact the least work of the job with the sticky letters.
One layer of paint is obvious too less. Between two and three you can see a slight difference and between three and four there is no difference at all. In the picture it looks like part four is lighter than part three, but that is because of the reflected light. So there will be three layers of paint as soon as all the letters have been stuck to the acrylic.