Change default 'Set featured image' text

// Change default 'Set featured image' text for any specific post type
add_action( 'current_screen', 'thisScreen' );

function thisScreen() {

    $currentScreen = get_current_screen();

    if( $currentScreen->post_type  === "YOUR_POST_TYPE" ) {
        add_filter( 'admin_post_thumbnail_html', 'new_html_text_for_feature_image' );
    }

}

function new_html_text_for_feature_image( $content ) {
    return $content = str_replace( __( 'Set featured image' ), __( 'Set banner image' ), $content);
}