I don't really understand what you mean. Yggdrasil will automatically discover and peer with other hosts running Yggdrasil on your network. Connecting your network, across the internet to another network is no different than connecting to a public peer.

My biggest concern with Yggdrasil is that, without careful configuration of every node, anyone can connect to your Yggdrasil network and potentially expose it to the public Yggdrasil network.

I've moved on to experimenting with Nebula (made by Slack). This is made specifically for closed networks and has built in tools to restrict access. I still REALLY like Yggdrasil and will continue to experiment with it; just not for private meshing.