Can I turn a single node simulator into a cluster?

Converting a single node into a cluster isn't a trivial undertaking. The biggest problem is that the System-ID for each node in a cluster must be different and as this is contained inside the disks themselves the setup.sh script cannot automate this in a simple manner.

It would be better to simply copy the data from your existing simulator into a freshly installed cluster. This has the advantage that it'll "just work" and means that your existing single-node simulator can be re-used or deleted as appropriate.