As I test I installed Kibana on a different server running on port 5602 with the default index changed from .kibana to .defaultindex2.
I can log in but after that Kibana shows
[security_exception] action [indices:admin/mappings/get] is unauthorized for user [kibana]
I think the problem is that the kibana system role only has access to .kibana* and not to .defaultindex2* but it doesn't appear you can change this role.
The Kibana instance running on the same server as Elasticsearch (port 5601, default .kibana index) does not have this problem.
How can I solve this problem?