How should prefabs be changed automatically based on updating a text file?

I'm currently using a text file to define data for a Monobehaviour. Ideally, any changes to the text file would result in calling an editor script to automatically update the Monobehaviour. My best guess of where to hook into the asset import pipeline is OnPostProcessAllAssets, but this leads to a few problems:

• The Monobehaviour's values are changed until the scene is deserialized:

     OnPostProcessAllAssets {
           // Find the game object & monobehaviour
           // Read the text file
           // Update the monobehaviour variables
           EditorUtility.SetDirty(theGameObject)
           EditorUtility.SetDirty(theBehaviour)
       }
  
  

  This seems to fail because Unity doesn't properly save the changes. The editor indicates that changes have been made, and they are lost upon either manually saving or playing the scene.

• Unity freezes:

     OnPostProcessAllAssets {
           // Find the game object & monobehaviour
           // Read the text file
           // Update the monobehaviour variables
           EditorUtility.SetDirty(theGameObject)
           EditorUtility.SetDirty(theBehaviour)
           EditorApplication.SaveAssets()
       }
  
  

  This causes the asset importer to enter an infinite loop, each time calling OnPostProcessAllAssets(). This happens regardless of using EditorApplication.SaveAssets() or AssetDatabase.SaveAssets(). However, when calling a function to perform the same action (via the MenuItem attribute), this works correctly; the problem is how to automate changes based on the text file being updated.

• Attempting to manage the number of times OnPostProcessAllAssets is called also fails to work, as the *.SaveAssets() methods don't appear to block or expose a means to wait until their completion. The number of times that OnPostProcessAllAssets is called is also indeterminate, and so counting also fails to achieve the results I'm after.

Similar questions include

• How can I create a custom import object. Like the questioner there, I'm hoping to do create updates at import instead of runtime. This question differs in that it asks about updating a prefab instead of creating new assets.

• Import own formats with asset importer similarly asks about creating new objects, not updating an existing asset.

• Custom Asset Files asks about creating objects programmatically using menu items, not automatically updating existing prefabs.

Is there a means to automatically update a prefab based on changes to a text file?