Concurrency settings and rate limits and other advanced preferences could read defaults from master when connecting. I.e. if not explicitly specified on peer node, use values from master.
An open question: how to specify the client settings on master? More command line arguments (effectively double the current ones, hnnngh...), or perhaps just a --client-defaults that points to a JSON file with the defaults? Or maybe --client-opts "<cli arguments in a string>".