I am the ghetto headlight/taillight mod master
Spray headlights: Sure, why not. If those GTO smoked covers are legal then the spray should be as well. As for the just the corner, some tape would work fine but it may look a bit retarded with only one side done [:I] Maybe a curved line working with the body of the car itself would look better.
The problem Im facing is the weathering of the spray. It may work well inside but outside it takes about 3 months of the rain and wind then scratches almost entirely off. Since I broke my taillight trying to take it apart last time Im going to rebuy some TYC lights and try again. This time with added clearcoat as a finish. My hopes are that this will keep the tint on longer, if not permanently.
I wont know the results for a while obviously, but if you dont mind redoing your work every few months go ahead and experiment. Dont worry about having to buy new headlights if it doesnt work out because alcohol and some cottom balls will easily remove the tint.