[NumLock]

блокирует вставку для Edit1:

Код:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    SaveWindowProc: TWndMethod;
  public
    { Public declarations }
    procedure TEditWindowProc(var Message: TMessage);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  SaveWindowProc:=Edit1.WindowProc;
  Edit1.WindowProc:=TEditWindowProc;
end;

procedure TForm1.TEditWindowProc(var Message: TMessage);
begin
  if Message.Msg=wm_paste then Message.Result:=0
  else SaveWindowProc(Message);
end;

end.