How to get an archive page meta?

From the get_post_meta() function reference, Retrieves a post meta field for the given post ID. The function is inteded to be used with posts (any type), not post type archives. You’ll need to dig into the documentation provided by the plugin author to find out, how to retrieve meta data for a post type archive.

Is it possible to change the permalink structure without changing the old permalinks to posts and without 301 redirects?

You can achieve that using a plugin like “Custom Permalinks“ The steps will be: 1- install and activate the plugin. 2- Save all your posts current permalinks into the custom meta field “custom_permalink” that meta field is the field that is used by the plugin to save the custom permalinks for each post and uses … Read more