facetwp.php

<?php

/**
 * FacetWP, singular name for post types
 *
 */
add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'filter_by_type' == $params['facet_name'] ) {

		$labels = array(
			'Pages'           => 'Page',
			'Cases'           => 'Case',
			'News'            => 'News Post',
			'Press Releases'  => 'Press Release',
			'Media'           => 'Document',
		);

		if( array_key_exists( $params['facet_display_value'], $labels ) )
			$params['facet_display_value'] = $labels[ $params['facet_display_value'] ];
    }
    return $params;
}, 10, 2 );