I got an easy solution on my question
here at
stackoverflow.com.
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Reza Aghaei: If you are going to add some custom verbs to designer of a Form, you need to create a new custom Designer by deriving from DocumentDesigner and overriding a lot of properties and method to recreate FormDesigner. As an easier solution, you can tweak designer of base form of your form. Let's say, you have Form1 and you want to have Do Something verb for it. To do so, if BaseForm is the base form for your Form1, it's enough to add the following code to BaseForm:
Protected Overrides Sub OnHandleCreated(ByVal e As EventArgs)
MyBase.OnHandleCreated(e)
Dim host = DirectCast(Me.Site.GetService(GetType(IDesignerHost)), IDesignerHost)
Dim designer = host.GetDesigner(Me)
designer.Verbs.Add(New DesignerVerb("Do Something", Sub(obj, args)
MessageBox.Show("Something done!")
End Sub))
End Sub
As a result, Do Something will be added to context menu for your Form1:
https://i.stack.imgur.com/j2L12.png