at the moment there is no such setting .. but I can understand that such a feature might be handy.
have a look at /src/xmltv.c .. around line 285 there is a function called xmltv_parse_channel.
There it parses the channel tag in the xmltv file. Maybe you can create a option the the xmltv settings to skip this globally (so for all channels)
or maybe you can make it an option in the channel list and then check against that option when tvheadend tries to load the data.
I suspect this happens aroud line 119 with the xmltv_load function.
So if you are up to a coding challenge ... hack up a solution and provide a patch.
Hein