In general you need to create a custom skill which is the same in every pack(to get examples you can look into the other armorset skills) and than attach it to a defined armorset of your custom stuff. If its in SQL so older chronicle than the armorsets sql table will be the file you search for, or if its a high5 l2j with translated armorsets to xml than data/stats/armorsets.xml and again look for examples how to add the skill there.