I would guess you will need to come at it from the bottom of the fender. Probably a contortionist act or fender removal if its standard GM engineering. Also, I'd wonder if the lamps are servicable or if they are LEDs. Might require you to replace the whole unit.
The hood signals are actually fiber optic cables that run to those fender pieces and then to the respective light. They have tabs on the bottoms of them that hold them in place to the fender. If you're *extremely* careful you can pop off one end and then they come out. My 89 Deville had them, they were brittle when one broke on me. I never found a way to access them from under the hood or bottom of the fender...only from the top of the fender, sadly.
I was able to find a replacement at a bone yard, for the one I broke, but I also broke the first one I tried to salvage. I painted it to match. Yes they are a luxury convenience, but I thought they were nifty.
Yea the feature is slick just wish they would have made replacement and repair easier. New question. As far as an 85 seville goes. Anybody got a damn clue how to remove the tail light housing?. I need to get dirt out of there big time.