I've been looking online for an answer, as my test environment is currently unavailable due to an upgrade, but while I know ('cuz it says in the conf file) that a restart is required when you change "archive_mode", is a restart or a reload required if the "archive_command" is changed? I seem to recall previously that I issued a reload after I changed this parameter and I saw in the logs that the new value had been recorded, but I'm not certain.