Can we resize (increase most probably) /etc/messages or messages.0.... messages.5 files? Like if we need to review a logs of a year ago? What if I need to check if a snapshot (snapmanager/native) had been created or not? Nowhere I could find that might be talked about that message file can be resized. However just willing to check it from a specific source.
Your best solution would be either to setup a logging server to capture the events on the filer to a separate server which you can customize to keep the logs for longer. Or you could copy the messages files themselves from the filer over to another server and then you can control how long the messages files are kept.
The messages files are used by the syslog deamon on the filer. You can control some things via the syslog.conf file.