As far as I know I don't think you can directly build "on top" of the existing internal Shopify web admin pages. The App Bridge or Embedded SDK allows you to create your own elements that are accessed via the Shopify web admin via its own iframe. See https://shopify.dev/tutorials/embed-your-app-in-the-shopify-admin for a quick rundown.
So it would be a taller task, in that you'd need to roll your own products view in order to allow display and manipulation of the metafield elements. Although if your intention is for viewing/modifying metafields one product at a time you could just build a basic form. The user provides the ID, the product is then displayed along with its metafield values piped into text boxes. If the user wants to modify any of these then they'd type the changes into the text boxes and hit a Submit button to commit the changes back into Shopify. Just some ideas...
