Can I allow Mac using Internet Sharing via Thunderbolt to talk to other devices on network? Does my MacBook - which is connected via Thunderbolt bridge to an iMac with Internet Sharing - see devices on the network the iMac is connected to?

I can see a new subnet is created on the Thunderbolt bridge adapter: 192.168.2.x

My main network is 192.168.1.x - the iMac is connected to this on Ethernet adapter.

Can I let the MacBook connect to other devices on the 192.168.1.x subnet?
I want to connect to a network share on another device in this upstream network.

Ideally:


I would be able to assign the MacBook with an (additional?) IP
address in the 192.168.1.x range.
Bonjour would be able to find
devices on the upstream network that had file sharing enabled, and
show them in the Finder sidebar.
Enabling Inter Sharing on your iMac makes it a NAT router. Its main purpose is to connect the downstream networks (192.168.2.0/24) to other networks (like your main router connects your internal network(s) to the internet). 

Your MacBook will connect to either other devices in the upstream network (192.168.1.0/24) or the Internet.

If you want to share a service on your MacBook (e.g. an Apache server) to the upstream network (192.168.1.0/24), you would have to forward the respective port on the iMac and add routes to the networks 192.168.2.0/24 on all other devices in the network 192.168.1.0/24.

Assigning an IP address of the 192.168.1.0/24 to the MacBook isn't possible.