From my own experience of installing graphite shafts a few years ago, my clubs ended up 4 – 5 swing weights lighter as Britt describes above. I invested in a swing weight scale and added 10 gram lead tip weights to the tips of the shafts to arrive at the original swing weight. I also shortened the tip of the shaft the width of the tip weight in an attempt to maintain the tip characteristics. I’m not sure if that was totally necessary. Also, moving from 115 grams to 75 grams is a significant jump. I ordered one 70 gram and one 80 gram shaft and installed them in my 7 and 8 iron and decided on 80 grams before ordering all the remaining shafts. Its a small incremental cost to ensure you are installing the correct shafts. Good luck.
no problem swapping graphite for steel. note that the Ping I200’s use a .355″ tip so you would need to select an replacement shaft (graphite or steel) with a .355 tip…or ream the hosels out to .370″ if there is a shaft that size you would want to install.