Block multiple categories from Blog

I found this code on this site by AshFrame which I added to my functions PHP file and works perfectly to stop one category being displayed on my blog (I have a custom menu so have the category displayed separately)…

add_action('pre_get_posts', 'block_cat_query' );

function block_cat_query() {
    global $wp_query;   
    if( is_home() ) {
        $wp_query->query_vars['cat'] = '-98';
    }
}

My question is how do I format this code to include a second category (in my case -92)? I tried duplicating the code but it generates a PHP error because you can only run the function once I think.