You can always drill off the heads, but that still leaves the stud of the bolt seized in the captive bracket moulded in the bumper, a seriously crap design imo.
A problem with fixing by taking the whole bolt off by cutting etc is the captive part in the bumper is not that strong, but I have fixed this once before for someone else.
I drilled off the heads, cut the bolt flush with the bumper material, then centre punch in centre of old bolt and drill out progressively to about 12-13mm direct through the old captive nut bracket.
I then used some 2mm flat bar 1/2" wide to make 2 "U" shaped brackets that were then put into the slot where the light goes.
Before I bent the brackets to a "U" shape I had drilled them to take a 4mm rivnut where the new SS bolt would once again secure the light, the brackets themselves were secured simply by way of the holes 2 top 2 bottom that had been drilled into them, and self tappers used, it meant the light fitted 2mm further out, but you couldn't see any difference once done, with the surround on.
tabetha