[Code]
procedure AppendFile(const SrcFile, DestFile: string);
var
  SrcStream: TFileStream;
  DestStream: TFileStream;
begin
  SrcStream := TFileStream.Create(SrcFile, fmOpenRead);
  try
    DestStream := TFileStream.Create(DestFile, fmOpenWrite);
    try
      DestStream.Seek(0, soFromEnd);
      DestStream.CopyFrom(SrcStream, SrcStream.Size);
    finally
      DestStream.Free;
    end;
  finally
    SrcStream.Free;
  end;
end;

procedure CurStepChanged(CurStep: TSetupStep);
begin
  // if the current step is post-installation (this is after the [Run] section has been processed), then...
  if CurStep = ssPostInstall then
    // do not hardcode file paths here; I don't know details to suggest a better way, but it's a wrong way
    AppendFile('C:\COBIAX\cobiax_path.lsp', 'C:\Program Files\Autodesk\AutoCAD 2016\Support\acad2016.lsp');
end;