id_duplicate_style.jsx

// duplication between sytle groups
// pstyle
// - group_a
//   - style_a2
//   - style_a1 <src>
// - group_b
//   - [style_a1 <dest>]
// 

#target indesign
var doc = app.documents[0];
var b = doc.paragraphStyleGroups.item("group_a").paragraphStyles.item("style_a1").duplicate();
b.move(LocationOptions.AT_END, doc.paragraphStyleGroups.item("group_b"));
b.name = "sytle_a1";