This thread is not about installing or replacing, but rather about removing, and removing avg2013flx seems to work as well as before.
~$ sudo dpkg -P -R avg2013flx
(Reading database ... 148706 files and directories currently installed.)
Removing avg2013flx ...
* Stopping avgd. [ ok ]
Uninstalling 'avgd' service initscripts...
Unregistering 'avgd' service ...
Removing any system startup links for /etc/init.d/avgd ...
Purging configuration files for avg2013flx ...
dpkg: warning: while removing avg2013flx, directory '/opt' not empty so not removed.
Processing triggers for man-db ...