Yes, you can change $actions array with your own function.

function your_function_name( $actions, $subscription ) {
    // here you can modify $actions array
    // 
    return $actions;
}

add_filter( 'wcs_view_subscription_actions', 'your_function_name', 15, 2 );

Yes, you can change $actions array in functions.php with your own function.

function your_function_name( $actions, $subscription ) {
    // here you can modify $actions array
    // 
    return $actions;
}

add_filter( 'wcs_view_subscription_actions', 'your_function_name', 15, 2 );