Just reporting the behavior I see. All my channels start off mapped to one XMLTV file #1.
If I do: Settings -> Channels (on the left) -> Advanced Tools -> Auto Map (to XMLTV file #2) = Nothing changes.
I verify this by: Settings -> Empty EPG then Update EPG. Which shows the EPG file being loaded.
If I do: Auto Map (to None) then Auto Map (to XMLTV file #2) = The associated XMLTV file is changed to file #2.