Can I Change The Sitemap Change Frequency?
This is an optional sitemap field to describe how often a URL is likely to be updated.
3.5.X and Newer
We’ve decided to remove the change frequency 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
You can change the frequency using the filter
'wpseo_sitemap_' . $filter . '_change_freq'.
It expects you to return one of the following values:
'always', 'hourly', 'daily', 'weekly', 'monthly', 'yearly', 'never'