It looks like a micro-type rear sight with a tall ramp front. Modifications of this type were common in the late-40's though the 50's for folks wanting adjustable sights for their big bore pistols. It looks well-done. Whether it affects value may depend on what brand it is, and who did the work. If it's Kings, collector value may remain constant or even rise a bit depending on the buyers preferences. If done by someone else, the value should drop some. If it's just for shooting, who cares?