gistfile1.php

<?php
// .com/achievements/
function fravaccaro_root_slug( $slug ) {
	return 'biscuits';
}
add_filter( 'dpa_get_root_slug', 'fravaccaro_root_slug' );

// .com/achievement/my_achievement/
function fravaccaro_singular_root_slug( $slug ) {
	return 'biscuit';
}
add_filter( 'dpa_get_singular_root_slug', 'fravaccaro_singular_root_slug' );