It's not very easy to find information on how to adjust debconf settings after a package has been installed and configured. Most of the information out there is for Debian developers wanting to add support for debconf in their maintainer scripts.
I ran into the problem of being unable to change a package's configuration options through dpkg-reconfigure and I found the following commands to do it manually:
debconf-show packagename
to show the list of debconf values that a package has stored,
echo "get packagename/pgsql/app-pass" | debconf-communicate
to query the current value of an option in the debconf database, and
echo "set packagename/pgsql/app-pass password1" | debconf-communicate
to change that value.
I'm not convinced that this is the easiest way for system administrators to manually lookup and modify debconf options, but that's the best I could find at the time.
I would use
debconf-get-selections | grep application > file
and edit the file, then use
debconf-set-selections < file
to load the changed settings.
This is as easy as it gets, as far as I'm aware; debconf-set-selections is different but not really any easier (do you know exactly what it does to seen flags?).
It would be possible to write some kind of shiny interface to edit the debconf database. I think that all the people who know debconf well enough to do this have probably avoided doing so because we're afraid that then people really would start treating it like an equivalent of the Windows registry.
If dpkg-reconfigure doesn't work, and if (more importantly) there isn't something in /etc you can edit instead of having to change values in debconf, then it's a bug in the package and should be reported as such.
You can edit /var/cache/debconf/config.dat manually instead, but be aware that you can really break things by editing this.
The file it uses for configuration is defined in /etc/debconf.conf, should it not be where you expect on your system