type
TCornerButton1 = class(TCornerButton);
TCornerButton2 = class(TCornerButton1);

TForm1 = class(TForm)
...
private
Button: TCornerButton2;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
Button := TCornerButton2.Create(self);
Button.Parent := self;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
Button.Free();
end;

TCornerButton2 = class(TCornerButton1);

TCornerButton2 = class(TCornerButton);

unit Unit1;

interface

uses
 System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
 FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, FMX.ExtCtrls;

type

 TCornerButton1 = class(TCornerButton)
   function GetDefaultStyleLookupName: string; override;
 end;

 TCornerButton2 = class(TCornerButton1)
   function GetDefaultStyleLookupName: string; override;
 end;

 TForm1 = class(TForm)
   procedure FormCreate(Sender: TObject);
 public
   Button: TCornerButton2;
 end;

var
 Form1: TForm1;

implementation

{$R *.fmx}

function TCornerButton1.GetDefaultStyleLookupName: string;
begin
 Result := 'buttonstyle';
end;

function TCornerButton2.GetDefaultStyleLookupName: string;
begin
 Result := 'buttonstyle';
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 Button := TCornerButton2.Create(self);
 Button.Parent := self;
end;

end.