Ive got some super old links that have a lot of SEO juice and I dont want to lose that if I change permalink structure. This is partly due to the older version of WP i have (2.1)
I want to use post ids in the structure now, and not the slug name or maybe both
myblog.com/post/12121/slug-name
If i use htaccess for this will Google and other search engines update their links without penalizing me?
Yes you need 301 redirection and you will carry on your SEO juice to the new URLs.