Conditionally Alter The Callout Content

function myprefix_custom_callout_content( $content ) {

	// Alter content for the portfolio posts
	if ( is_singular( 'portfolio' ) ) {
		return 'MY CUSTOM CONTENT';
	}
	
	// Return content
	return $content;

}
add_filter( 'wpex_get_footer_callout_content', 'myprefix_custom_callout_content' );