What's the best way to update the /etc/systemd/journald.conf file?

[sdwilsh]

I want to modify the retention of journald, and to do so, I need to update /etc/systemd/journald.conf (which does not persist). I can add the updated file in the boot stage, but systemd-journald is already running, so I'd have to reload it at that point. However, systemctl only supports enable, disable, mask, or start. I could just run a command, but that feels a bit hacky. Am I missing a better solution?