Customize the Featured Image labels

change_featured_image_labels.php

<?php
/**
 * Changes strings referencing Featured Images for a post type
 * 
 * In this example, the post type in the filter name is "employee" 
 * and the new reference in the labels is "headshot".
 *
 * @see 	https://developer.wordpress.org/reference/hooks/post_type_labels_post_type/
 *
 * @param 		object 		$labels 		Current post type labels
 * @return 		object 					Modified post type labels
 */
function change_featured_image_labels( $labels ) {

	$labels->featured_image 	= 'Headshot';
	$labels->set_featured_image 	= 'Set headshot';
	$labels->remove_featured_image 	= 'Remove headshot';
	$labels->use_featured_image 	= 'Use as headshot';

	return $labels;

} // change_featured_image_labels()

add_filter( 'post_type_labels_employee', 'change_featured_image_labels', 10, 1 );