After looking closely it doesn't seem that it's possibly to easily replace an audio file in a project with a new file. I know about the "Update Mastering Files" option for when you are also using Song Mode but I am not using Song Mode.
Let's say you are just using Project Mode and a client sends you a new mix of a song you've already mastered. I expected to be able to right click on a file in the project and choose "Replace" and point to the new file but I can't find any such feature.
Is this a missing feature or am I missing something?