I don't understand the problem fully.
Simply load a track having \\ in a field e.g. and edit it in the main window. You'll see it change to ", ".
e.g.
Click the Description field, press RETURN. See:
Do you want to use "\\" as literal characters?
I am using them as literal characters, entered using another app. I want Mp3tag just not to mess that up.
Where do you see "\\" displayed as ", "? At the main window
Yes.