環境
Unity: 2020.2.6f1
OS: Windows
今回のコード
露光などの詳細なカメラの設定はカメラ設定にはなく, SerializedPropertyをつかって取得と代入をする必要がある。
SerializeにはUnityが内部で使っていたSerializedHDCameraクラスをコピペして利用した。
Test.cs
using System;
using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEditor.Rendering;
using UnityEngine;
using UnityEngine.Rendering.HighDefinition;
namespace CameraUtil
{
    public class Test : MonoBehaviour
    {
        [SerializeField] private int iso;
        /// <summary>
        /// Updateで行うべきではない
        /// スライダーなどのイベントに割り当ててください
        /// </summary>
        private void Update()
        {
            var serialize = new SerializedObject(Camera.main);
            SerializedHDCamera serializedHdCamera = new SerializedHDCamera(serialize);
            serializedHdCamera.Update();
            // 値の代入
            serializedHdCamera.iso.intValue = iso;
            serializedHdCamera.Apply();
        }
    }
    class SerializedHDCamera
    {
        public SerializedObject serializedObject;
        public SerializedObject serializedAdditionalDataObject;
        //public SerializedProperty backgroundColor;
        public SerializedProperty iso;
        public SerializedProperty shutterSpeed;
        public SerializedProperty aperture;
        public SerializedProperty bladeCount;
        public SerializedProperty curvature;
        public SerializedProperty barrelClipping;
        public SerializedProperty anamorphism;
        public SerializedProperty exposureTarget;
        public SerializedProperty antialiasing;
        public SerializedProperty SMAAQuality;
        public SerializedProperty taaSharpenStrength;
        public SerializedProperty taaHistorySharpening;
        public SerializedProperty taaAntiFlicker;
        public SerializedProperty taaMotionVectorRejection;
        public SerializedProperty taaAntiRinging;
        public SerializedProperty taaQualityLevel;
        public SerializedProperty dithering;
        public SerializedProperty stopNaNs;
        public SerializedProperty clearColorMode;
        public SerializedProperty backgroundColorHDR;
        public SerializedProperty xrRendering;
        public SerializedProperty passThrough;
        public SerializedProperty customRenderingSettings;
        public SerializedProperty clearDepth;
        public SerializedProperty volumeLayerMask;
        public SerializedProperty volumeAnchorOverride;
        public SerializedProperty allowDynamicResolution;
        //public SerializedFrameSettings frameSettings;
        public CameraEditor.Settings baseCameraSettings { get; private set; }
        // This one is internal in UnityEditor for whatever reason...
        public SerializedProperty projectionMatrixMode;
        public SerializedProperty probeLayerMask;
        public SerializedHDCamera(SerializedObject serializedObject)
        {
            this.serializedObject = serializedObject;
            projectionMatrixMode = serializedObject.FindProperty("m_projectionMatrixMode");
            var additionals = CoreEditorUtils.GetAdditionalData<HDAdditionalCameraData>(serializedObject.targetObjects,
                InitDefaultHDAdditionalCameraData);
            serializedAdditionalDataObject = new SerializedObject(additionals);
            var hideFlags = serializedAdditionalDataObject.FindProperty("m_ObjectHideFlags");
            // We don't hide additional camera data anymore on UX team request. To be compatible with already author scene we force to be visible
            if ((hideFlags.intValue & (int) HideFlags.HideInInspector) > 0)
                hideFlags.intValue = (int) HideFlags.None;
            serializedAdditionalDataObject.ApplyModifiedProperties();
            //backgroundColor = serializedObject.FindProperty("m_BackGroundColor");
            iso = serializedAdditionalDataObject.FindProperty("physicalParameters.m_Iso");
            shutterSpeed = serializedAdditionalDataObject.FindProperty("physicalParameters.m_ShutterSpeed");
            aperture = serializedAdditionalDataObject.FindProperty("physicalParameters.m_Aperture");
            bladeCount = serializedAdditionalDataObject.FindProperty("physicalParameters.m_BladeCount");
            curvature = serializedAdditionalDataObject.FindProperty("physicalParameters.m_Curvature");
            barrelClipping = serializedAdditionalDataObject.FindProperty("physicalParameters.m_BarrelClipping");
            anamorphism = serializedAdditionalDataObject.FindProperty("physicalParameters.m_Anamorphism");
            exposureTarget = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.exposureTarget);
            antialiasing = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.antialiasing);
            SMAAQuality = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.SMAAQuality);
            taaSharpenStrength =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.taaSharpenStrength);
            taaQualityLevel = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.TAAQuality);
            taaHistorySharpening =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.taaHistorySharpening);
            taaAntiFlicker = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.taaAntiFlicker);
            taaMotionVectorRejection =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.taaMotionVectorRejection);
            taaAntiRinging = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.taaAntiHistoryRinging);
            taaQualityLevel = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.TAAQuality);
            dithering = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.dithering);
            stopNaNs = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.stopNaNs);
            clearColorMode = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.clearColorMode);
            backgroundColorHDR =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.backgroundColorHDR);
            xrRendering = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.xrRendering);
            passThrough = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.fullscreenPassthrough);
            customRenderingSettings =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.customRenderingSettings);
            clearDepth = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.clearDepth);
            volumeLayerMask = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.volumeLayerMask);
            volumeAnchorOverride =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.volumeAnchorOverride);
            // frameSettings = new SerializedFrameSettings(
            //     serializedAdditionalDataObject.FindProperty("m_RenderingPathCustomFrameSettings"),
            //     serializedAdditionalDataObject.Find((HDAdditionalCameraData d) =>
            //         d.renderingPathCustomFrameSettingsOverrideMask)
            // );
            probeLayerMask = serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.probeLayerMask);
            allowDynamicResolution =
                serializedAdditionalDataObject.Find((HDAdditionalCameraData d) => d.allowDynamicResolution);
            baseCameraSettings = new CameraEditor.Settings(serializedObject);
            baseCameraSettings.OnEnable();
        }
        public void Update()
        {
            serializedObject.Update();
            serializedAdditionalDataObject.Update();
            // Be sure legacy HDR option is disable on camera as it cause banding in SceneView. Yes, it is a contradiction, but well, Unity...
            // When HDR option is enabled, Unity render in FP16 then convert to 8bit with a stretch copy (this cause banding as it should be convert to sRGB (or other color appropriate color space)), then do a final shader with sRGB conversion
            // When LDR, unity render in 8bitSRGB, then do a final shader with sRGB conversion
            // What should be done is just in our Post process we convert to sRGB and store in a linear 10bit, but require C++ change...
            baseCameraSettings.HDR.boolValue = false;
        }
        public void Apply()
        {
            serializedObject.ApplyModifiedProperties();
            serializedAdditionalDataObject.ApplyModifiedProperties();
        }
        internal static void InitDefaultHDAdditionalCameraData(HDAdditionalCameraData cameraData)
        {
            var camera = cameraData.gameObject.GetComponent<Camera>();
            cameraData.clearDepth = camera.clearFlags != CameraClearFlags.Nothing;
            if (camera.clearFlags == CameraClearFlags.Skybox)
                cameraData.clearColorMode = HDAdditionalCameraData.ClearColorMode.Sky;
            else if (camera.clearFlags == CameraClearFlags.SolidColor)
                cameraData.clearColorMode = HDAdditionalCameraData.ClearColorMode.Color;
            else     // None
                cameraData.clearColorMode = HDAdditionalCameraData.ClearColorMode.None;
        }
    }
}