Cannot use object of type stdClass as array
You are able to change menu attributes using Menu Attributes module . If any customization is needed on top of that then you can follow the below process.

You can able to override theme links using theme_menu_link in template.php. Follow below step to override.


Go to your active theme folder might be in sites/all/theme or if you are using default theme then themes folder
Go to the active theme folder
Look for template.php
Override theme_menu_link by copy pasting entire function and replacing theme with your theme name.
Do your changes inside function wherever necessary!