Index: export.php
===================================================================
--- export.php	(revision 37384)
+++ export.php	(working copy)
@@ -534,6 +534,17 @@
 			 */
 			if ( apply_filters( 'wxr_export_skip_postmeta', false, $meta->meta_key, $meta ) )
 				continue;
+			
+			/**
+			 * Filter for modifying post meta before it is exported.
+			 *
+			 * @since 4.6.0
+			 *
+			 * @param string $meta_value     Current meta value.
+			 * @param object $meta           Current meta object.
+			 * @param object $post           Current post object.
+			 */
+			$meta->meta_value = apply_filters( 'wxr_export_postmeta', $meta->meta_value, $meta, $post );
 		?>
 		<wp:postmeta>
 			<wp:meta_key><?php echo wxr_cdata( $meta->meta_key ); ?></wp:meta_key>