For some hair rigs you're going to have problems. For those where all the hair is grouped in the "head" actor (typical for short cuts) it should just work if the hair was rigged exactly as V4, but some of the more complex ones probably need some adjustment - riggers typically didn't adjust scale parameters for all bones adjacent to the head, so for things like braids or ponytails you may need to go back to the vendor to get an update, or learn how to make this adjustment yourself.

Note if you're in Poser 8+, don't change any scale settings on the hair itself, just check the "Include scales" checkbox on the BODY of the hair figure, for conformers.  For prop hair, it should already be loading as a child of the Head, which should already include scale changes as the head is scaled, although it might need to be shifted around a bit.

My Freebies