Filter alch_default_page_icon should be used to change the default AO options pages icon. The default value is the AO logo. The passed value should be compatible with the $icon_url parameter of the function.
Example
function change_default_page_icon() {
return 'dashicons-chart-pie';
}
add_filter( 'alch_default_page_icon', 'change_default_page_icon' );
To modify the page icon on a per-page basis use the hook.
