Option Explicit
Private Declare Function GetClassName& Lib "user32" Alias "GetClassNameA" (ByVal hwnd&, ByVal lpClassName$, ByVal nMaxCount&)
Private Declare Function AccessibleObjectFromWindow& Lib "oleacc" (ByVal hwnd&, ByVal dwId&, riid As GUID, xlWB As Object)
Private Declare Function GetDesktopWindow& Lib "user32" ()
Private Declare Function GetWindow& Lib "user32" (ByVal hwnd&, ByVal wCmd&)
Private Const GW_HWNDNEXT = 2
Private Const GW_CHILD = 5
Private Const OBJID_NATIVEOM = &HFFFFFFF0
Private Type GUID
    lData1 As Long
    iData2 As Integer
    iData3 As Integer
    aBData4(0 To 7) As Byte
End Type
Private IDispatch As GUID, oWnd As Window
Public Sub AddReference()
    Dim i&
    With IDispatch
        .lData1 = &H20400: .iData2 = &H0: .iData3 = &H0
        .aBData4(0) = &HC0: .aBData4(1) = &H0: .aBData4(2) = &H0
        .aBData4(3) = &H0: .aBData4(4) = &H0: .aBData4(5) = &H0
        .aBData4(6) = &H0: .aBData4(7) = &H46
    End With
    Referece2AllWorkbooks 0, "EXCEL7", 0, 0, 0, Application.UserLibraryPath & "MyFunction.xla"
    Set oWnd = Nothing
End Sub
Private Function Referece2AllWorkbooks&(hWndStart&, ClassName$, level&, lHolder&, lCnt&, sFile$)
    Dim hwnd&, sWindowTitle$, sClassName$, wb as Workbook
    If level = 0 Then
        If hWndStart = 0 Then
            hWndStart = GetDesktopWindow()
        End If
    End If
    
    'Increase recursion counter
    '--------------------------
    level = level + 1
    
    'Get first child window
    '----------------------
    hwnd = GetWindow(hWndStart, GW_CHILD)
    
    Do While hwnd > 0
        'Search children by recursion
        '----------------------------
        lHolder = Referece2AllWorkbooks(hwnd, ClassName, level, lHolder, lCnt, sFile)
        
        'get the class name
        '------------------
        sClassName = Space$(255)
        r = GetClassName(hwnd, sClassName, 255)
        sClassName = Left$(sClassName, r)
        
        If sClassName Like ClassName & "*" Or sClassName = ClassName Then
            Referece2AllWorkbooks = hwnd
            lHolder = hwnd
            AccessibleObjectFromWindow hwnd, OBJID_NATIVEOM, IDispatch, oWnd
            If Not oWnd Is Nothing Then
                If oWnd.Visible Then
                    lCnt = lCnt + 1
                    On Error Resume Next
                    For Each wb In oWnd.Application.Workbooks
                        wb.VBProject.References.AddFromFile sFile
                    Next
                End If
            End If
        End If
        
        'Get next child window
        '---------------------
        hwnd = GetWindow(hwnd, GW_HWNDNEXT)
    Loop
    Referece2AllWorkbooks = lHolder
    
End Function

Private WithEvents App As Application
Private pathXlam As String
Private Sub Workbook_Open()
    Set App = Application
    Dim ref, Wbs As Workbook
    For Each ref In Application.VBE.VBProjects
        If ref.Name = "VBAProjectUserListBox" Then pathXlam = ref.Filename: Exit For
    Next ref
    
    On Error Resume Next
    For Each Wbs In Workbooks
        Wbs.VBProject.References.AddFromFile pathXlam
    Next Wbs
End Sub
Private Sub Workbook_AddinUninstall()
    Dim ref, Wbs As Workbook
    For Each Wbs In Workbooks
        For Each ref In Wbs.VBProject.References
            If ref.Name = "VBAProjectUserListBox" Then Wbs.VBProject.References.Remove ref
        Next ref
    Next Wbs
End Sub
Private Sub App_WorkbookOpen(ByVal Wb As Workbook)
    On Error Resume Next
    Wb.VBProject.References.AddFromFile pathXlam
End Sub
Private Sub App_WorkbookBeforeClose(ByVal Wb As Workbook, Cancel As Boolean)
    Dim ref
    For Each ref In Wb.VBProject.References
        If ref.Name = "VBAProjectUserListBox" Then Wb.VBProject.References.Remove ref
    Next ref
End Sub