Actually, you might be able to get the result you need by stopping the current MMC service, changing that value, then restarting MMC:
/etc/init.d/MultimediaConsole.sh stop
setcfg myidbserver ENABLE false -f $(getcfg SHARE_DEF defVolMP -f /etc/config/def_share.info)/.system/idbserver.conf
/etc/init.d/MultimediaConsole.sh start
This should make MMC reload the config files and apply their settings.