That SPARQL Form page is added by the Virtuoso Authentication Layer (VAL VAD) installation which you must have in place in the indicated Virtuoso 8.1 installation, and the HOWTO: Modify Virtuoso default /sparql endpoint Form page using XSLT document is only for the Virtuoso old and new default SPARQL ENDPOINT form page in the post. I am check internally how the VAL specific SPARQL Form page can be customised …