Desactivar el botón Cerrar de un formulario

Solo haz dos botones "Command1 y Command2"
Option Explicit
Private Declare Function GetSystemMenu Lib "user32" _
(ByVal hWnd As Long, ByVal bRevert As Long) As Long
Private Declare Function ModifyMenu Lib "user32" Alias "ModifyMenuA" _
(ByVal hMenu As Long, ByVal nPosition As Long, _
ByVal wFlags As Long, ByVal wIDNewItem As Long, _
ByVal lpString As Any) As Long
Private Declare Function DrawMenuBar Lib "user32" _
(ByVal hWnd As Long) As Long
'
Private Const MF_BYCOMMAND = &H0&
Private Const MF_ENABLED = &H0&
Private Const MF_GRAYED = &H1&
'
Private Const SC_CLOSE = &HF060&
Private Sub Command1_Click()
' Deshabilitar el botón de cerrar el formulario
Dim hMenu As Long
'
hMenu = GetSystemMenu(hWnd, 0)
Call ModifyMenu(hMenu, SC_CLOSE, MF_BYCOMMAND Or MF_GRAYED, -10, "Close")
'
Call DrawMenuBar(hWnd)
'
End Sub
Private Sub Command2_Click()
' Habilitar el botón de cerrar el formulario
Dim hMenu As Long
'
hMenu = GetSystemMenu(hWnd, 0)
Call ModifyMenu(hMenu, -10, MF_BYCOMMAND Or MF_ENABLED, SC_CLOSE, "Close")
Call DrawMenuBar(hWnd)
'
End Sub