It should work with existing hair groups. Make sure the skull cap (or whatever you hade the hair grown on) then run the script. The first list is the hair groups. Select the one you want to work with. Then you can either select nothing and work with the whole group, select individual strands in the second list, or create a selection and select some strands that way. I don't believe the select Y locks was ever working properly. 

What the script doesn't work with is previous styling. It will override the growth controls and the styling tool. You can use the styling tools afterwards if you need to adjust sonething afterwards.

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