Patch binary files (Replace a string in a file with new string) with delphi

// Patch binary files / Replace a string in a file with new string.

procedure TForm1.Button1Click(Sender: TObject);
var
  f: file;
  l: Longint;
  FileName, oldstring, newstring, s: string;
begin
  oldstring := 'old string';
  newstring := 'new string';
  FileName  := 'c:\YourFileName.xyz';

  s := oldstring;
  AssignFile(f, FileName);
  Reset(f, 1);
  for l := 0 to FileSize(f) - Length(oldstring) - 1 do
  begin
    Application.ProcessMessages;
    Seek(f, l);
    BlockRead(f, oldstring[1], Length(oldstring));
    if oldstring = s then
    begin
      Seek(f, l);
      BlockWrite(f, newstring[1], Length(newstring));
      ShowMessage('String successfully replaced!');
    end;
    Application.ProcessMessages;
  end;
  CloseFile(f);
end;