Can I Change the Sitemap Priority?
This is an optional sitemap field that informs search engines which pages you consider more important than other pages on your site.
3.5.X and Newer
After talking to some Googlers, we’ve decided to remove the priority variables from our XML Sitemaps in the 3.5 version of Yoast SEO as Google has said publicly that they don’t use them on most sites.
Version 3.4.X and earlier
The following filters are available for changing the sitemap priority:
'wpseo_xml_post_type_archive_priority'. The filters are documented in the class-sitemaps.php file.
Advanced User Tip: You can find a great tutorial for implementing this filter here.