Hi Larry
We have something similar to the 337 do but not for Strobes.
Excuse is when you add or do something on the wing, it's a aerodynamic surface, can't be touched unless an structure engineer take a look at it or more precisely make a whole fuc%?&$... production out of it to eventually make a LSTC for on particular aircraft. Lstc: Limited STC. I have one for my prop. Costed me 1500.00 to put the wooden 150 h.p. on the 165... Even if you have exact same wing profile on 14-19 that has STC. Like Kevin said about the feds, Better be legal then safe.
The field aproval here is called a Major mod conformity report.
The american 337 will work if it refer to an STC or manufacturer drawing. I have some on my aircraft that was done when it was in USA and they're all OK but the strobe one...
I had to do a conformity report for the radio installation as they was no entry done on installation. That was OK.
Alain.