I've got 3 of each for "testing", fletched and non fletched in AK. I found that with the application of some of the old style ferrule cement "hot melt" glue, rubbed on the insert, I could sand it to friction fit and stay put when pulling from a bag target filled with plastic.
That way, I could keep adding those Gold tip all-thread and weights w/o changing the shaft length, or if showing too weak, switch to alum. insert to lighten things.
Got me in the ballpark before I cut anyhting.
Shimming out the riser sideplate also helped diagnose when it was too weak...
So there's lots of ways to mess with the arrow w/o cutting it to change spine.
I just never was comfortable with the "nock orientation" when it stuck in the target to define spine...given that I've never found a totally homogenous target medium that assured me that the arrow wasn't being diverted when it struck becuase of the medium it was slamming into. Just my oneriness I guess.