Yes, if you wish to add addtional options or addons to your Hosting account you can do so at all times from the Client Area. Here is how to do this.
1. Login to Client Area
2. Goto "My Services"
3. Find your domain and hosting plan.
4. Click on the little icon with arrow to the right.
5. You are now in the Product Details, scroll to bottom to "Account Addons"
6. Click on "Upgrade/Downgrade Options"
7. Choose your addons and click button "Click to Continue" and follw checkout instructions.