I wrongly assumed that @Elpie meant to make a Child Theme.
Therefore my answer now becomes that I suggest making a Child Theme of Twenty Ten to a. protect your changes for future updates and b. still have all the benefits that Twenty Ten offers now and in the future.
To do so, you will also need to duplicate the twentyten folder and give it a different name. You also need to change the top part of the Twenty Ten style.css
In the top of your style.css you will need to tell that you still use twentyten as the parent theme. So you will need to add a line:
Also at the top, but under the initial code you should import the twentyten stylesheet. You can do that by using this line of code:
Eventually the top of your stylesheet should look similar to this:
Theme Name: Twenty Ten Child
Description: Child theme for the Twenty Ten theme
Author: Your name here
All this and more on Child Themes in the Codex: http://codex.wordpress.org/Child_Themes