Switching to GossipingPropertyFileSnitch Causes Connection Refusal - cassandra

Question

I have brand new install of Cassandra 3.0.9 on CentOS 7.4.1708.
I am trying to change from the default SimpleSnitch to GosspingPropertyFileSnitch.
When I try and follow the steps on the DatStax Website, it appears as though I should only have to change the endpoint_snitch setting in the cassandra.yaml file. When I do that and restart the cassandra service, I am no longer able to connect to cassandra with nodetool or cqlsh (Connection Refused). Changing the settign back to the SimpleSnitch yields no reversal and ability to connect. I am confused as to what settings I am missing that are causing this to happen. I'd like to know
What I am missing in trying to get it moved to the GossipingPropertyFileSnitch?
Why changing the setting back does not revert things to its previous state where I can connect using nodetool or cqlsh?
I have two nodes in the cluster, both of which I want to act as seeds.
cassandra.yaml: - Node 1
cluster_name: '<My Cluster Name>'
- seeds: "<IP Add1>, <IP Add2>"
listen_address: <IP Add1>
rpc_address: <IP Add1>
endpoint_snitch: GossipingPropertyFileSnitch
#broadcast_address: 1.2.3.4
cassandra.yaml: - Node 2
cluster_name: '<My Cluster Name>'
- seeds: "<IP Add1>, <IP Add2>"
listen_address: <IP Add2>
rpc_address: <IP Add2>
endpoint_snitch: GossipingPropertyFileSnitch
#broadcast_address: 1.2.3.4
cassandra-rackdc.properties - Node 1:
dc=<DC1 Name>
rack=rack1
prefer_local=true
cassandra-rackdc.properties - Node 2:
dc=<DC1 Name>
rack=rack2
prefer_local=true
cassandra-topology.properties - Both Nodes:
<IP Add1>=<DC1 Name>:RAC1
<IP Add2>=<DC1 Name>:RAC2
In CQLSH - Both Nodes
UPDATE system.local SET cluster_name = '<My Cluster Name>' where key='local';