Hoss7504
Don't do it, if you like the 3 wood without tip trim.
Leave the 5 wood shaft 3/4" longer than you like. If it's too flexible then pull the shaft and tip off 1/2".
If it play good ( which I think will be the case ) then blow off the grip and trim to length .
I had seen both in sets of fairway woods and hybrids where the flex played different, because of the what you're thinking of. 5 wood will be shorter than the 3 wood so it'd play stiffer with shorter length anyway.