Yes, you can use Menu Writer to update the PowerStore menu.
You will need to create a site for PowerStore where the CSSMenuWriter folder is at the root of your site. Then open the Templates folder, and open the Main.dwt.php file. Click on the Menu in Design View and Then in the Property Inspector (Window -> Properties), you should see three buttons. click the edit Theme button to make changes to the design of the menu.
We don't have a doc for updating the powerstore menu, but here is a link to the MenuWriter support page:
let me know if you have any other questions.