convert one tag to category via mysql

Hello

I have blog with Tags and Categories, and I want to “convert” one tag to category. How it can be done:

1. Create new category Y (X – old tag)

2. Join all posts with tag X to category Y (via MYSQL)

3. Remove tag X from all posts (via MYSQL)

4. Setup htaccess redirect from this tag to new category (to prevent 404 for links from other websites and google)

Question: how I can do 2 and 3? Or may be you know other way?