Added Custom post to have both before transparent and before stack. Created reference image for Postprocessing test

Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom.unity

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     lightMeter:
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       height: 256
     vectorscope:
       size: 256
       exposure: 0.12
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+      motionGridSize: 64
+      colorBlindnessType: 0
+      colorBlindnessStrength: 1
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-  m_BeforeTransparentBundles: []
+  m_BeforeTransparentBundles:
+  - assemblyQualifiedName: InvertOpaque, Assembly-CSharp, Version=0.0.0.0, Culture=neutral,
+      PublicKeyToken=null
   m_BeforeStackBundles:
   - assemblyQualifiedName: HalfToneOpaque, Assembly-CSharp, Version=0.0.0.0, Culture=neutral,
       PublicKeyToken=null

Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Main Camera Profile.asset

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Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Materials/TransparentMat_opaque.mat

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-  m_ShaderKeywords: _ALPHABLEND_ON _GLOSSYREFLECTIONS_ON _METALLIC_SETUP _SPECULARHIGHLIGHTS_ON
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         m_Scale: {x: 1, y: 1}
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Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Scripts/HalftoneOpaque.shader

 
         #include "../../../../../../../PostProcessing/PostProcessing/Shaders/StdLib.hlsl"
 
-        TEXTURE2D_SAMPLER2D(_MainTex, sampler_MainTex);
-         TEXTURE2D_SAMPLER2D(_Pattern, sampler_MainTex);
+        //TEXTURE2D_SAMPLER2D(_MainTex, sampler_MainTex);
+        Texture2D _Pattern;
+        Texture2D _MainTex;
+        SamplerState sampler_MainTex;
+        SamplerState sampler_Pattern;
+        //TEXTURE2D_SAMPLER2D(_Pattern, sampler_MainTex);
         float _Blend;
         float _Scale;
         float _Steps;
         	
             float4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord);
             float luminance = 1 + dot(color.rgb, float3(0.2126729, 0.7151522, 0.0721750)) * 0.25;
-            float3 pattern = SAMPLE_TEXTURE2D(_Pattern, sampler_MainTex, i.texcoord * (_ScreenParams.xy * _Scale * luminance)).rgb;
+            float3 pattern = SAMPLE_TEXTURE2D(_Pattern, sampler_Pattern, i.texcoord * (_ScreenParams.xy * _Scale * luminance)).rgb;
             color.rgb = round(((pattern.rrr)-_Blend) + (color * _Steps)) / _Steps;
             return color;
         }

ImageTemplates/LightweightPipeline/Scenes/027_PostProcessing.unity.png.meta

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Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Scripts/InvertOpaque.cs

+using System;
+using UnityEngine;
+using UnityEngine.Rendering.PostProcessing;
+
+[Serializable]
+[PostProcess(typeof(InvertOpaqueRenderer), PostProcessEvent.BeforeTransparent, "Custom/LWtest/Invert Opaque")]
+public sealed class InvertOpaque : PostProcessEffectSettings {
+    public BoolParameter enable = new BoolParameter();
+}
+
+public sealed class InvertOpaqueRenderer : PostProcessEffectRenderer<InvertOpaque> {
+
+	public override void Render(PostProcessRenderContext context){
+		var sheet = context.propertySheets.Get(Shader.Find("Hidden/Custom/LWtest/InvertOpaque"));
+		context.command.BlitFullscreenTriangle(context.source, context.destination, sheet, 0);
+	}
+
+}

Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Scripts/InvertOpaque.cs.meta

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Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Scripts/InvertOpaque.shader

+Shader "Hidden/Custom/LWtest/InvertOpaque"
+{
+	HLSLINCLUDE
+
+        #include "//Assets/PostProcessing/PostProcessing/Shaders/StdLib.hlsl"
+
+        TEXTURE2D_SAMPLER2D(_MainTex, sampler_MainTex);
+
+        float4 Frag(VaryingsDefault i) : SV_Target
+        {
+        	
+            float4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord);
+            return 1-color;
+        }
+
+    ENDHLSL
+
+    SubShader
+    {
+        Cull Off ZWrite Off ZTest Always
+
+        Pass
+        {
+            HLSLPROGRAM
+
+                #pragma vertex VertDefault
+                #pragma fragment Frag
+
+            ENDHLSL
+        }
+    }
+}

Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/028_PostProcessing_Custom/Scripts/InvertOpaque.shader.meta

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