AssetPostprocessor.OnPreprocessAudio()

説明

Add this function to a subclass to get a notification just before an audio clip is being imported.

これによりインポート設定をコードにより制御できます。

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

public class MyAudioPostprocessor : AssetPostprocessor
{
    void OnPreprocessAudio()
    {
        if (assetPath.Contains("mono"))
        {
            AudioImporter audioImporter = (AudioImporter)assetImporter;
            audioImporter.forceToMono = true;
        }
    }
}