To understand why FMOD Studio behaves the way you’ve observed you need to understand that FMOD Studio can’t see what your operating system is doing. It can see what files are in your projects’ assets folder, but that’s all the information it has.
For example, if you rename a file using your operating system’s interface, FMOD Studio can tell that the filename it expected to see is gone and a filename it didn’t expect to see has appeared, but it has no way of knowing why; I can’t tell whether you renamed a file or whether you deleted one file and added an new one. Similarly, if you edit an existing file or replace it with an identically-named file, FMOD Studio has no way of knowing that the file has changed, and so doesn’t know that it needs to reload the file from disk in order to play back the new version.
Fortunately, it is possible to let FMOD Studio know about changes made to files through your operating system.
If you replace an asset file on disk with an identically-named file, or edit and save an existing asset file, you can tell FMOD Studio to re-load the file and update the version of it used in events by right-clicking on the changed files in the Assets Browser to open the context-sensitive menu, then selecting the ‘Refresh’ menu item. (This feature existed in earlier versions of FMOD Studio than 1.08, but it sounds like you’re not familiar with it.)
If you want to replace an asset file with a new version that has a different file name, there’s a simple process you can follow. First, copy the new file into the appropriate location in the assets folder. Then, in the Assets Browser, multiselect both the old file and the new file, right-click on the new file to open the context-sensitive menu, and select the ‘Consolidate…’ menu item. This replaces all your project’s references to the old file with references to the new file.