It looks like a nodetool repair is needed after increasing your RF. I guess that a cleanup has to be performed after decreasing the RF to remove useless replica.
2011/12/5 A J <firstname.lastname@example.org>
If I update a keyspace to increase the replication factor; what
happens to existing data for that keyspace ? Does the existing data
get automatically increase its replication ? Or only on a RR or node
repair does the existing data increase its replication factor ?