Nice set up. With the addition of a pattern on either side of the spinning beam and the use of EDM Tracer guides on the chainsaw bar, matching the original profile or making multiple posts the same would be easy. The original post being replaced could be ripped in half to make the pattern or a new profile could be created using 2x material. The chain saw would have to be kept at 90 deg. to the post or the cut would not match the pattern. the post could be turned by hand, having a helper to turn the post while you are cutting would be ideal.
Similar to this router set up for an eight sided boss pin

Not all who wander are lost.