Change the prefix to all Drupal tables.

add-table-prefix.php

<?php

// ------------------------------------------------------------------------------------------
// This simple script adds the specified table prefix to all tables in the current DB.
// It is used if you want to add a prefix to all tables once the DB has been created.
//
// WARNING: Do not run on a DB which already uses prefixes to separate different databases.
//
// To run copy this script to the docroot of your Drupal installation and then do:
//
//  $ drush scr add-table-prefix.php
//
// Assumptions:
//
//   * You are NOT using a multi site environment
//   * You have Drush configured and running
//   * You have a single site in sites/all/
//
// DISCLAIMER: If this code breaks your site don't blame me! You should understand how this
//             works before running it. Also don't run this on a production server withoug
//             having done tests on another server.
// ------------------------------------------------------------------------------------------


// This is prefix you want your tables to have.
$prefix = 'xyz123';

// Read all tables
$result = db_query("SHOW TABLES");
  
if ($result) {
  while ($row = $result->fetch(PDO::FETCH_NUM)) {

    // rename table
    $table_old = $row[0];
    $table_new = $prefix . '_' . $table_old;
    db_query("RENAME TABLE {$table_old} TO {$table_new}");

    // show progress
    print "  $table_old -> $table_new\n";
  }
}