If you are talking about WinForms: the best systematic explanation of how you go about adding design-time support for things like Actions and Designer Verbs in a custom control I've come across is in the 2004 edition of Matthew MacDonald's "Pro .NET 2.0 Windows Forms and Custom Controls in C#" (APress).
On CP check out:[
^].
On MSDN:[
^]
This is, imho, a non-trivial task.
You might keep in mind that defining a public Enum, and then putting a public property in your custom control,
whose type is the type of that public Enum will result in the presence
in the Properties Editor at design-time ... for an instance of that custom control dragged onto a Form ... in a ComboBox selection for that entry in the Properties Editor.
That's an easy win.
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