Yes, Modbus spec is limited to 247 addresses but Unilogic will let you use the full binary 1-255. I've never actually connected more than 247 devices so I don't know what would happen.
Those shoes you're talking about are mine, and I've never had a problem walking in them. You're only going to end up with conflicts if you screw up the addressing. So far I've managed to count into the mid 200's without hurting myself. Uniapps alone would clue you in to which devices are in conflict if there is one, let alone any basic in-program diagnostics.
The built-in master is running about 200 small sensors (Dwyer temp/humidity/co2 devices). Each only has 4-6 operations. It's lightweight data-wise; just a long string of devices. Low polling rates, updates only once every few seconds. We've set these networks up many times before with no problems. Surprisingly durable even when the network topology is abused.
The reason we need such a heavy operations load is our I/O network is comprised of a fleet of Click PLCs (small, cheap, durable, modular devices from Automation Direct). Unfortunately dollar-per-I/O it's a better deal than the local or remote expansion kits, or even the EX-RC1. ((EDIT: We use the Click PLCs because if they lost communications to the Unistream they can act autonomously))
Each one handles a ton of environmental and facility control systems. Easily 200 operations each. The max for the 02RSC is 512 operations. While it means we're burning off an entire modbus master on effectively two or three slaves I don't know another way around it. Also, many of these devices would end up in completely different parts of the facility and having seperate networks would simplify the wiring.
There are no gateways, so far everything has been a direct connection back to the unistream.
So the original question: How are the 232 ports, when configured in Unilogic as Modbus masters, different from the 485 port? I'm guessing the hardware inside the module isn't strictly speaking a serial comm port (5v-15v logic, single ended, etc) but rather it's emulating those characteristics.