I would compromise by running the following line (in /home/pi)
then /home/pi is the home directory, with config files. /home/pi/hdd is /media/hdd, and you don't have to fiddle with anything.
If you really want /media/hdd as the home dir, you would hit problems if ever the pi came up and /media/hdd wasn't there. You can do that sore of thing to yourself with usermod (man usermod) but what I'm suggesting is safer. This way, if the disk isn't there, it's a "no such file or directory" error.