Hi Zhen Yuan, you have to clone the group form_container on the group form_clone and put this vbs code on the button:
Dim oItem, oParent, oClone
Set oItem = XDocument.DOM.selectSingleNode("/my:myFields/my:Form_Container")
Set oClone = XDocument.DOM.selectSingleNode("/my:myFields/my:Form_Clone/my:Form_Container").cloneNode(true)
Set oParent = oItem.parentNode
oParent.replaceChild oClone, oItem
If you had choose to modify by rules (on click), because you have to reinitialize the field one by one. It can take several second and if you add some field, you have to had rules.
With this method, if you add some fied, you don't need to change anything, it suppose to work directly.
I think that 15 seconds on the load is acceptable.