Enforcing a specific transition configuration for all transitions in a RuntimeAnimationController

AnimatorControllerTool.cs

using UnityEngine;
using UnityEditor;
using System.Text.RegularExpressions;
using System.IO;

// Drop this in some Editor folder
public static class AnimatorControllerTool {

	[MenuItem("CONTEXT/RuntimeAnimatorController/Enforce Transition Settings")]
	public static void FixTransitions(MenuCommand command)
	{
		var path = AssetDatabase.GetAssetPath(command.context);
		path = Regex.Replace(path, "^Assets", Application.dataPath);
		AssetDatabase.StartAssetEditing();
		try
		{
			// We can't use serialization to read the properties, so we rely on editing the asset text file instead
			// This naturally requires asset files to be serialized as text
			// You can achieve this by Edit/Project Settings with Asset Serialization Mode set to Force Text
			var txt = File.ReadAllText(path);
			txt = Regex.Replace(txt, @"(?<param>m_HasExitTime:\s+)\d+", "${param}0");
			txt = Regex.Replace(txt, @"(?<param>m_HasFixedDuration:\s+)\d+", "${param}1");
			txt = Regex.Replace(txt, @"(?<param>m_TransitionDuration:\s+)[\.\d]+", "${param}0");
			txt = Regex.Replace(txt, @"(?<param>m_TransitionOffset:\s+)[\.\d]+", "${param}0");
			File.WriteAllText(path, txt);
		}
		catch(System.Exception e) { Debug.LogException(e); }
		AssetDatabase.StopAssetEditing();
		AssetDatabase.Refresh();
	}
}

BEWARE that this operation can be really destructive as it manually overwrites parts of the asset data in a really hacky way. So backup your asset before attempting this!