It is extremely easy to add as many tags as you need to at once in a WordPress blog, even without using some special plugin.

1) Create a post (no need to publish it),

2) At the tags input field of your post editing page, paste all the tags that you need separated by commas,

3) Add the tags to the post, by pressing enter on your keyboard, or by clicking the form button, and update the post.

That’s it! You can now delete this post completely, or just remove its tags association, keeping your newly created tags in the blog ready to be used in other posts. To associate particular tags from your list with posts in your database automatically, you can use this auto tagger plugin.