how to insert it in the function in tags fields in edit post?

Hello to all in the wordpress comunity. I have a function that mix strings in a array:

function gen_num()
{
global $post;
$mixnames = get_post_meta( $post->ID, ‘fieldnames’, true );

if ( ” == $mixnames ) {
$input = array(“Neo”, “Morpheus”, “Trinity”, “Cypher”, “Tank”);
$rand_keys = array_rand($input, 2);
$mixnames = $input[$rand_keys[1]];
update_post_meta( $post->ID, ‘fieldnames’, $mixnames );
}
// DISPLAYS THE OUTCOME
print $mixnames;
}
1- I insert it in the output the_content post, and I also enter the tags field (meta tag of posts), how do? already tried something in the wordpress structure that suggests it was metatag but not see anything! I want to fill that field tags on the right side of the post edit.

2- A curiosity, because the values that this function inserted in the body of the post, in the_content, do not appear on the dashboard in edit mode of posts? because not can bring up for me to do SEO for SEO plugin by Yoast, when I’m in edit mode I would like to edit things according to the plugin indicates, but on the site it appears, but in edition mode appears only what I wrote manually the posts! the values I call the above function not appear! because?

Thanks to all. Best Regards.