only removing/renaming the .hts directory under the hts users home dir should be enough. But you should do this when tvheadend is not running. so first stop tvheadend then remove/rename. When tvheadend starts, it reads the epgdb file into memory and keeps it there. When it shuts down it saves the EPG from memory back into the epgdb file again.
So there is no need to reinstall tvheadend each time.
Also, try to see if you can create an smaller xmltv file with only the suspect tv stations epg data in it. You can do that with a simple text editor by removing the other sections from the xmltv file.
Hein