Append to post

Is it possible to append custom text to a post on publishing a post?

I am able to add info to custom fields on publishing using “add_action(‘publish_post’, ‘add_custom_field_automatically’);” and “add_post_meta($post_ID….” based on tags added to the post so was wondering if I could include some custom text at the end of the post too, but only on publishing?

Thanks is advance