Переопределить параметры формы при её создании

unit MainFrm;

interface

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

type
  TMainForm = class(TForm)
    btnClose: TButton;
    procedure btnCloseClick(Sender: TObject);
  private
    { Private declarations }
  protected
    // Capture the WM_NCHITTEST message to enable moving the form.
    procedure WMNCHitTest(var message: TWMNCHitTest); message WM_NCHITTEST;
  public
    { Public declarations }
    procedure CreateParams(var Params: TCreateParams); override;
end;

var
  MainForm: TMainForm;

implementation

{$R *.DFM}

procedure TMainForm.WMNCHitTest(var message: TWMNCHitTest);
begin
  inherited;
  message.Result := HTCAPTION;
end;

procedure TMainForm.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  Params.Style := WS_THICKFRAME or WS_POPUP or WS_BORDER;
end;

procedure TMainForm.btnCloseClick(Sender: TObject);
begin
  Close;
end;

end.