Tagging Old Posts

Hi all,

I want to start tagging my posts and have a list of about 50 tags that I want to enter into WordPress. Instead of using the UI, I just want to write to the tables “terms” and “taxonomy” appropriately. So, when I post new posts, the relationships are automatically created and the posts are tagged as pert the terms I will create. This is easy enough.

My trouble is, what about my past posts? Is there any plugin or easy method to tag all the posts from the past as per the terms I will define?

Thanks!