I have to say I like when hair is modifiable by normal SL editing methods as it is nice to be able to move a strand or two one way or another. BUT I also love the convienience of resize scripts in hair to do the main editing.
So a little find I have made is really useful. It is called Script Injector and Script Cleaner. As hair can be made of a zillion prims (hyperbole much!) - tho much is over 100 prims, it is not a nice thought to need to place the resize script in every prim. Script Injector puts in your script into all the prims (of course the controller script need only go into the root prim). So if you have hair, shoes, skirt oh anything that is mod you can pop in your resize script to all prims with ease.
Script Injector does not include a resize script - it is only the script for dropping scripts - but in my opinion a great little script to own.
It costs $500L for a retaillers version (so you can sell the item if you are a creator) and $250L for personal use.
It is normally found at The Tatty Theatre but this shop is closed for the moment so you can only find this script on Xstreet - use this link: https://xstreetsl.com/modules.php?name=Marketplace&MerchantID=70848