Вы хотите пункт меню именно Excel ( Развернуть, свернуть и т.д.) или же менб из семейства CommandBars. Если 2 то так :
Public Sub CreateMenu()
dim YourMenu As CommandBar
Dim tmpCommandBar As CommandBar
const MNUNAME as string="YourMenu"

For Each tmpCommandBar In Application.CommandBars
If tmpCommandBar.Name = MNUNAME Then
CommandBars( MNUNAME).Delete
Exit For
End If
Next


Set YourMenu = CommandBars.Add(Name:= MNUNAME
, Position:=msoBarTop, MenuBar:=False, temporary:=True)




With YourMenu.Controls.Add(msoControlButton)
.Style = msoButtonIconAndCaption
.BeginGroup = True
.Caption = "Ля-ля-ля"
.OnAction = "SomeAction"
.FaceId = 548
End With


YourMenu.Visible = True
End Sub
public sub SomeAction
msgbox "Ля-ля-ля"
end sub
Если надо не панель а замена меню тогда
Set YourMenu = CommandBars.Add(Name:= MNUNAME
, Position:=msoBarTop, MenuBar:=True, temporary:=True)

Так это не имеет отношения к Excel. Юзайте API для работы с меню.
Вот пример из апплемана
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function AppendMenu Lib "user32" Alias "AppendMenuA" (ByVal hMenu As Long, ByVal wFlags As Long, ByVal wIDNewItem As Long, ByVal lpNewItem As String) As Long
Private Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Long, ByVal bRevert As Long) As Long
Private Const MF_STRING = &H0
Private Const SCOFFSET = 2000
Private Sub YourMenu()
Dim H As Long, M As Long, M1 As Long
H = FindWindow("XLMAIN", vbNullString)
M = GetSystemMenu(H, False)
M1 = AppendMenu(M, MF_STRING, SCOFFSET, "Menu")
End Sub
Хотя я бы не стал лазить в системное меню - у сабжа есть свои панели.

ПРавильно
Public Function YourFunction () as string
YourFunction="Hello"
end function