if you’re using the shafts are already installed in your irons (parallel or taper tip), what you do is move your 5 iron shaft into the 6 iron head, the 6 iron shaft into the 7 Iron head, etc. The 5 iron shaft is a bit longer than your old 6 iron shaft and you could then trim the butt so it’s at your original 6 iron length. In essence your moving a more flexible shaft into the head (ie. a five iron shaft isn’t tip trimmed as much as a six iron shaft).
If your installing new parallel tipped shafts, you simply trim the 6 iron shaft as though it was a 5 iron (more flexible), trim the 7 iron shaft as though it was a 6 iron, and so on. Butt trim to length.
If you’re using taper tip shafts, you would purchase a 5 iron shaft to install into the 6 iron, etc and butt trim to length.
Butt trimming a shaft doesn’t have that much affect on flex of the shaft. the greatest effect comes from tip trimming. soft stepping will have about 1/3 cpm change in flex (softer, more flexible).
Excellent question ping guy.