How do I change the wording of Wordpress's default activation emails?

Hi,
I want to change the wording of the activation email sent out when you sign up for a store on my site. I want to change it from saying.
"To activate your blog" to "To open your store".
I also want to pretty it up which I understand the HTML Email Templates plugin will do but will that allow me to change the content?

Regards,
Nat.