Can't recall the years for retooling, if it is, it should encase the entire bust. so either retooling or Machine Doubling, no added value Maybe coop will jump in and post his images of retooling or you can search it in the glossary and search box
Re-tooling was used during that time. The master hub was showing weakness and the master dies were altered a bit.
On the wheat cents some 1953 cents were enhanced:
So on the die it should make it raise a bit, but not exactly looking like the true design. On this coin though I feel it is Machine Doubling. Note that all of that area is affected. So I lean towards Machine Doubling.