Different ads on every website on multisite environment

Question

I am using following code to insert ad in article, after 8th paragraph, through functions.php file:

add_filter( 'the_content', 'prefix_insert_post_ads' );
  
function prefix_insert_post_ads( $content ) {
      
    $ad_code = '<div>Ads code goes here</div>';
  
    if ( is_single() && ! is_admin() ) {
        return prefix_insert_after_paragraph( $ad_code, 8, $content );
    }
      
    return $content;
}
   
   
function prefix_insert_after_paragraph( $insertion, $paragraph_id, $content ) {
    $closing_p = '</p>';
    $paragraphs = explode( $closing_p, $content );
    foreach ($paragraphs as $index => $paragraph) {
  
        if ( trim( $paragraph ) ) {
            $paragraphs[$index] .= $closing_p;
        }
  
        if ( $paragraph_id == $index + 1 ) {
            $paragraphs[$index] .= $insertion;
        }
    }
      
    return implode( '', $paragraphs );
}

Every webisite on network has different ad code, but in the same time I am using same theme on all sites, thus - only one functions.php file. I know I can create multiple child-themes for every installation, but that is not an option here.

Is there any way to use above code for multisite environment, but to add code to only one, general functions.php file?

Thank you...