That thread was about ModeShape 2.x, which does lots of things in a completely different way. Therefore, there is no corresponding configuration setting akin to the "system store" in 2.x.
Can you please post your ModeShape 3 and Infinispan configurations and your exception so that we can evaluate what is going on? If you are not able to start a repository due to an error such as "Error converting String to a Name", then my guess (without enough information) would be that you're not persisting any information (via Infinispan cache store or by running Infinispan in distributed mode), so that upon startup your custom namespaces are not being found.
Sorry for the late response - my error was caise by not having a valid first line in my cnd file e.g.
putting the correct line for my file (based on your cnd definition) fixed my error.