Function to update_post_meta by blog

I am really stuck… a bit new to multisite and don’t know the functions yet.

I am looking to have a pretty big form that a user fills out to register a site and then have the information used to populate custom fields in posts on the new site.

The site is being built from a template so I know exactly what posts will exist after creation. I was hoping that using a redirect would work to redirect before executing the update_post_meta() function tied to the form but that was no bueno.

What I am essentially looking for is an update blog post meta function that would include a blog id in it or something, does one exist?