Sadly, I'm lower than a noob when it comes to Debian... I'm a 'buntu man, and while they're close relatives, they're not the same. So see if this helps, but it may be useless!
On Ubuntu, you can usesudo service to start/stop/restart tvheadend... maybe the same holds true on Raspbian. So I could stop tvheadend with this and then restart it from the command line with different options.
I can't test it for you as I'd break my live system while it's being used, but try this...
If you do a ps -eaf | grep tvheadend first, you'll see the command line for tvheadend, and you can then run the equivalent from the command line, e.g.
$ ps -eaf | grep tvheadend
hts 1933 1 5 Jan30 ? 02:52:00 tvheadend -f -u hts -g video
ian 4999 4893 0 16:28 pts/4 00:00:00 grep --color=auto tvheadend
$ sudo service tvheadend stop
$ sudo tvheadend -f -u hts -g video -C
The ps tell me that it's currently running as a daemon: the -f tells the process to fork into the background. It's also running as user hts (-u) and group video (-g).
If you need to do some testing and make this -C work on reboot, the key elements are the upstart job in /etc/init - there's a file called tvheadend.conf that physically starts the tvheadend process. But that in turn looks at a config file, /etc/default/tvheadend. The last line of this allows you to set specific command-line arguments, e.g.TVHARGS="-C"_
By all means, have a play around and post some results back here, and I'll see if I can help!