AssetDatabase.SetImporterOverride

Задает конкретный импортер, который будет использоваться для ассета.

К одному ассету можно привязать несколько импортёров — через список переопределяющих расширений или через составные расширения.

using UnityEngine;
using UnityEditor;
using UnityEditor.AssetImporters;
using UnityEngine.Assertions;

public class AssetDatabaseExamples : MonoBehaviour
{
    [MenuItem("AssetDatabase/Example Importer Actions")]
    static void AllImporterActions()
    {
        //This sets CubeImporter to be used for the asset
        AssetDatabase.SetImporterOverride<CubeImporterOverride>("Assets/CompanionCube.cube");
        Debug.Log("New importer: " + AssetDatabase.GetImporterOverride("Assets/CompanionCube.cube"));

        //This clears importer override and sets it to null
        AssetDatabase.ClearImporterOverride("Assets/CompanionCube.cube");
        // This asset does not have an Importer Override anymore. The Default Importer is used ( CubeImporter ).
        Assert.IsNull(AssetDatabase.GetImporterOverride("Assets/CompanionCube.cube"));
    }
}

//This importer is the Default Importer for the .cube extension.
[ScriptedImporter(1, "cube")]
public class CubeImporter : ScriptedImporter
{
    public override void OnImportAsset(AssetImportContext ctx)
    {
        var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        var position = new Vector3(0, 0, 0);
        cube.transform.position = position;
    }
}

//This importer is the Default Importer for the .composite.cube extension.
[ScriptedImporter(1, "composite.cube")]
public class CompositeCubeImporter : ScriptedImporter
{
    public override void OnImportAsset(AssetImportContext ctx)
    {
        var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        var position = new Vector3(1, 1, 1);
        cube.transform.position = position;
    }
}

//This importer is an Override Importer for the .cube extension.
[ScriptedImporter(1, null,new []{ "cube" })]
public class CubeImporterOverride : ScriptedImporter
{
    public override void OnImportAsset(AssetImportContext ctx)
    {
        var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        // 'cube' is a GameObject and will be automatically converted into a prefab
        ctx.AddObjectToAsset("main obj", cube);
        ctx.SetMainObject(cube);
    }
}