Changing Permalink Structure

ths is not a definitive answer, but i don’t think you have to duplicate your database.

you may have to hand-edit your .htaccess file by using 301 redirects. if you have edited your permalinks, you have an .htaccess file in your home directory. and you want to add the new redirects ‘outside’ of wordpress’s own redirect rules.

see this: https://www.cre8asiteforums.com/viewtopic.php?p=139141

yours would be like this:

redirect 301 /year/month/date/slug https://www.you.com/archives/postnumber

see also: https://www.tamingthebeast.net/articles3/spiders-301-redirect.htm

best of luck and pls tell us how you resolve this, since i will have to do this at some stage too!