I would:
Mask off on both sides of the seam; first paint masking tape, then several layers of duct tape or packing tape.
Since I'm a woodworker, I would make up a fixture out of plywood with a slot that I could center over the seam and figure out a way to make blocking so I could clamp it in place.
Score through the seam a couple of times with a sharp knife.
Use a Multimaster or similar vibrating cutter with a fine saw blade to cut through the filler, then use the same tool and blade to cut away as much filler as possible without scoring the steel.
All of this is done through the slotted plywood-that way, it would be nearly impossible (nearly but not completely!) to slip out of the seam and damage the paint.
Once it was cut through and as much as possible was removed, I would remove the fixture, keep the heavy masking at both sides, then clean up the balance with files and sandpaper.
If I decided to seam seal it again, I would prime it then seal, keeping the sealer much deeper into the seam (no where near the face of the seam).
Unmask, feather the edges, remask, prime, and touchup spray.
With any luck at all, you will be able to cut and polish the touchup into the existing SS without respraying the entire panel.
Anyway, I am new at this game, so I may be all wet here. It won't hurt my feelings at all if the more experienced guys disagree with me.