How to disable transpose shortcut?
These emacs-style shortcuts -- like ^T for transpose -- are defined for the entire OS's text system in /System/Library/Frameworks/AppKit.framework/Resources/StandardKeyBinding.dict.

To override the shortcuts, Apple suggests:


  To customize bindings, you create a file named DefaultKeyBinding.dict in ~/Library/KeyBindings/ and specify bindings to augment or replace the standard bindings. You may use the standard bindings file as a template. It is recommended that you use the Property List Editor application to edit a bindings dictionary. You may use another application such as TextEdit or Xcode, but if you do you must ensure the encoding of the saved file is UTF8.


Source: https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/EventOverview/TextDefaultsBindings/TextDefaultsBindings.html