1. Configure agent etc/zabbix_agentd.conf
For example:
Server= your server or proxy IP
ServerActive=your active server or proxy IP
Hostname=new_host
HostMetadataItem=test.key
UserParameter=test.key,echo "new registered host"

2. Configure frontend:
Create Autoregistration action
Condition: Host metadata contains host
Operation: Add host

3. Run server and agent (+ proxy if it is proxy test case)
4. Go to Data collection -> Hosts
5. Observe that new_host was added to the list
6. Stop server and agent
7. Delete discovered host
8. Run server and agent again
9. Observe:

For 6.2:
new_host is added again immediately

For 6.4:
new_host is NOT re-added again
change Hostname to new_host_1 in etc/zabbix_agentd.conf
restart agent
new_host_1 is NOT added
change UserParameter to test, echo "new123 registered host"
change Action Condition to Host metadata contains new123
restart agent, wait a little
And finally new_host_1 is added

For 6.4-proxy:
new_host is NOT re-added again
change Hostname to new_host_1 in etc/zabbix_agentd.conf
restart agent
observe that new_host_1 is added