You could weld it without removing it for sure. Might damage it some in the process though. Really comes down to whether or not it needs replaced to begin with imo. If it's solid than weld away, if it's rotten or soft, weld and then replace it.
For larger holes ( nickel size or bigger ) I'd get a piece of aluminum plate cut to fill in most of the area of the hole & have it welded in. This mainly has to do with the skill & experience of the welder involved. It never hurts to get an opinion from the welder on what can be done.