Best posts made by esan

@blastframe Ok was able to retrofit your version to get what I wanted, a bit of guesswork in here, but got the result im after lol

import c4d
from c4d import gui

def createInstance():
    obj = op.GetDown()
    inst = c4d.BaseObject(c4d.Oinstance) # created Instance with Base Object
    inst[c4d.INSTANCEOBJECT_LINK] = obj # set Instance's reference link
    # set the name using the object passed to the function
    inst[c4d.ID_BASELIST_NAME] = "%s Instance"%obj[c4d.ID_BASELIST_NAME]
    return inst # return the Instance instance

def AddLongDataType(obj): # create User Data Container named Picker
    if obj is None: return

    bc = c4d.GetCustomDataTypeDefault(c4d.DTYPE_LONG)
    bc[c4d.DESC_NAME] = "Picker"

    doc.AddUndo(c4d.UNDO_CHANGE, obj)
    obj.AddUserData(bc)

    c4d.EventAdd()

def setQuickTab(obj, inst, data): # change User Date container to type Cycle, populate with Children Names
    descid = data[0][0]
    bc = data[0][1]

    children = obj.GetChildren()

    # Build new cycle options container dynamically
    cycle = c4d.BaseContainer()

    for i,child in enumerate(children):
      cycle.SetData(i, child.GetName())

    bc[c4d.DESC_CYCLE] = cycle

    doc.AddUndo(c4d.UNDO_CHANGE, obj)
    # Set modified description data container
    inst.SetUserDataContainer(descid, bc)

def main(doc):
    obj = doc.GetActiveObject()
    if (obj == None):
        gui.MessageDialog("Please select the Root of the Assets you wish to Instance.")
        return

    doc.StartUndo()
    inst = createInstance()
    doc.InsertObject(inst)
    AddLongDataType(inst)
    data = inst.GetUserDataContainer()
    setQuickTab(obj, inst, data)
    
    doc.AddUndo(c4d.UNDO_NEW, inst)
    doc.EndUndo()
    c4d.EventAdd()

if __name__=='__main__':
    main(doc)