You really have to try this out and see. I can only answer from what I read in the ref docs.

> Do I need to ConfiguredGraphFactory.close(GRAPH) before I update its configuration?
The docs say the binding between graph name and graph instance renews every 20 secs, so maybe this is not necessary.

> What happens to GRAPH_TEMP? Wouldn't it be still pointing to the same storage backend HBase table as GRAPH, i.e. to TABLE_B?
GRAPH_TEMP is just a name in the JanusGraphManager memory. It does not matter.

> if I want to reuse the same scheme, I'd have to have some logic that the next time around I need to renew GRAPH, I have GRAPH_TEMP talk to TABLE_A instead and then switch GRAPH to use TABLE_A, correct?
You are right. I would prefer straight versioning or a timestamp in the tablename, or the reuse of names will bite you some day. Of course, you would drop TABLE_A from the storage backend if not needed anymore.

Best wishes,   Marc