Not entirely sure if it will help, but if you want to do permanent redirects and you have access to the .htaccess, I found out how to do them for my sites. This post may help you:
https://theaffiliatemarketer.net/improve-page-rank-with-htaccess/
It will give you a basic idea, but I think you’ll need more than that. What you need to do is to get the old URLs 301 (permanently) redirected to the new URLs. You’ll probably need to rewrite the URLs before the WordPress rules are applied.
