You guys are going on and on about a pre-existing bolt being upgraded. Nobody mentioned the scrap yard of old bolts, hangers, holes, glue, engine parts, etc. at the top of Jello tower (look down at your feet when glaring at this (brand new) 5 year old bolt next time).
Most of the old bolts and pins in the area were installed because that was the only way to protect there before modern cams were invented. Think: old bolt on the S. Face of Jello Tower. Or, old bolt(s) on classic crack, etc.
It's OK to replace failing/ worn bolts if they were installed there at the time of the first ascent, and cannot be protected nearby with removable gear. This is probably pretty rare.
I think the bolts on Old Grey Mare have been replaced recently? If so, that's a pretty good example.