I want to add hairstyles from "aniceoaktrees hairstyles" and from "apachii skyhair" mods to custom "children race".
launch "forgotten construction set.exe"
select mods with hairstyles that you want to import then select mod where you want to add these hairstyles. last modified mod should be "active" (it's custom race mod).
navigate to "Races", find desired race (in my case "Greenlander Child"), double-click.
open "hairs" from drop menu, click "add". choose hairstyles that you want to be added.
save your mod file.