Sí.
Obtienes el handle del menú con GetSystemMenu().
Inhabilitas el item, llamando a ModifyMenu() MF_BYCOMMAND/SC_SIZE/MF_GRAYED
using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
private UInt32 MF_BYCOMMAND = 0;
private UInt32 MF_GRAYED = 1;
private UInt32 SC_SIZE = 0xF000;
[DllImport("user32.dll")]
private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);
[DllImport("user32.dll")]
private static extern bool ModifyMenu(IntPtr hMnu, UInt32 uPosition, UInt32 uFlags, IntPtr uIDNewItem, string lpNewItem);
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
IntPtr sysMenu = GetSystemMenu(this.Handle, false);
ModifyMenu(sysMenu, SC_SIZE, MF_BYCOMMAND | MF_GRAYED, IntPtr.Zero, "Tamaño");
}
}
}
Imports System.Runtime.InteropServices
Partial Public Class Form1
Inherits Form
Private MF_BYCOMMAND As UInt32 = 0
Private MF_GRAYED As UInt32 = 1
Private SC_SIZE As UInt32 = &HF000
<DllImport("user32.dll")> _
Private Shared Function GetSystemMenu(hWnd As IntPtr, bRevert As Boolean) As IntPtr
End Function
<DllImport("user32.dll")> _
Private Shared Function ModifyMenu(hMnu As IntPtr, uPosition As UInt32, uFlags As UInt32, uIDNewItem As IntPtr, lpNewItem As String) As Boolean
End Function
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim sysMenu As IntPtr = GetSystemMenu(Me.Handle, False)
ModifyMenu(sysMenu, SC_SIZE, MF_BYCOMMAND Or MF_GRAYED, IntPtr.Zero, "Tamaño")
End Sub
End Class
