If reproduced with correct stamping font, I don't see the issue with restamping it. If pics to document it are kept, then stamping becomes a backup for down the road if the documents are lost. Like when paint marks or stripes are added to a part during restoration it could be considered "fishy" since we are trying to pass off the part as original. Now, restampng a VIN number I would not condone. I suppose one could use very small font and stamp "decked" above the restamping if they wanted to feel warm and fuzzy.