Provide a filter:
$my_item = apply_filters(
'plugin_name_item_args',
array(
'post_title' => $item->get_title(),
'post_content' => '',
'post_status' => 'publish',
'post_excerpt' => $item->get_description(),
'post_type' => 'post'
),
$item # pass the $item object to the filter
);
A plugin can change these values now with:
add_filter( 'plugin_name_item_args', 'another_plugin_filter', 10, 2 );
function another_plugin_filter( $args, $item )
{
$args['post_type'] = 'page';
return $args
}