Where is the code that adds a blog to Pro Site Level?

I am attempting to create an action hook that runs after site activation, using some custom meta I will add to the signup page with selected level. The goal is so after a user activates their site via activation email, the hooked function will run and add the new site to the Pro Site at the level passed in via meta. Does this make sense?

So I am trying to find code to grab and how to bring it in from the Pro Sites plugin.

I am using this code snippet someone shared in another thread,

require_once(WP_PLUGIN_DIR . '/pro-sites/pro-sites.php');
$psObj = new ProSites();
$proLevel = $psObj->get_level();

To be able to adjust what people see via their level, so that works. Is there a function I can call in a similar fashion to add a new site to Pro Sites level?