I want to move my blog from its original domain (site1.com) to become a sub-domain on another domain which is a multisite installation (sub1.site2.com).
I also want to change the permalink structure on the new site based on some SEO suggestions I read online. Original used
/%year%/%monthnum%/%category%/%postname%/ as its permalink structure. I want to switch to
posts/%category%/%postname%/as the new permalink structure on sub1.site2.com . I am changing the permalinks because I rightfully agree with some SEO suggestions that articles may feel dated if the year is prominent in the URL when actually the content is mostly not time dependent.
How do I use either
.htaccess or a plugin or even PHP (as in this thread) to ensure links from the old site (posts, category and other archives) do not break especially because of the the change in permalink structure.
I tried following a few previously answered questions but got confused becasue of the nature of their specific queries. Also Regex syntax is relatively new to me so I want to defer to people who know what they are doing fully.