Mythtv-setup has two huge drawbacks when dealing with channel edits. First you can only edit one channel at a time and removing a channel means setting the option "visible" to off. Don’t ever delete a channel; it will come back with a vengeance on the next channel scan. Hiding the channel is the only good option, as it also keeps the scheduler from trying to record any show even if it has valid EPG data.
If your channel list is big, and having DVB-S in Europe with the LNB pointing to Astra you are talking about a thousand channels, this is very frustrating. Especially because after changing a channel's settings one is send back to the top of the list, requiring you to skip all the way down again. If you ever have to edit more than one channel this way you will loose all your hair.
The second option is to use the web front-end mythweb. There you can change all the settings, of all channels at once. Now picture my rather underpowered server trying to build a PHP based list of over 1000 channel. This is how it looks:
There are many solutions to those quirks, but for now there is a quick and dirty solution to the problem. The following SQL statement updates a set of channel numbers to visible. Changing the value 1 to 0 of visible you can hide a channel from MythTV. Changing the values of channum makes it possible for you to set the range of the edit. My prefered frontend to mysql is phpMyAdmin, but even the commandline utilities are just as good.
UPDATE `channel` SET `visible` = '1' WHERE `channum` > 300 and `channum` < 400;
Hope this keeps frustration low.
MythTV 0.20 is still a bitch when you need to remove channels from it. Even more so when you need to remove more than 5 channels, since both GUI options available (mythtv-setup and mythweb) are subobtimal for their own reasons, I was inclined to find a third.