Replacement Shaders & Shader Keywords

ReplacementShaderTest.cs

using UnityEngine;
public class ReplacementShaderTest : MonoBehaviour
{
    public Shader replaceShader;
    private string[] KeyWords = new string[] { "UV_VIS", "LOCAL_POS_VIS", "WORLD_POS_VIS", "DEPTH_VIS", "LOCAL_NORMAL_VIS", "WORLD_NORMAL_VIS" };

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.A))
            GetComponent<Camera>().SetReplacementShader(replaceShader, ""); // All objects will have shader applied on it
        else if (Input.GetKeyDown(KeyCode.W))
            GetComponent<Camera>().SetReplacementShader(replaceShader, "MyTag"); // Only objects which have shaders that have a sub-shader that has a tag called "MyTag"
        else if (Input.GetKeyDown(KeyCode.S))
            GetComponent<Camera>().ResetReplacementShader(); // Removes all applied replacement shaders
        else if (Input.GetKeyDown(KeyCode.Z))
            EnableKeyWord(0);
        else if (Input.GetKeyDown(KeyCode.Alpha1))
            EnableKeyWord(1);
        else if (Input.GetKeyDown(KeyCode.Alpha2))
            EnableKeyWord(2);
        else if (Input.GetKeyDown(KeyCode.Alpha3))
            EnableKeyWord(3);
        else if (Input.GetKeyDown(KeyCode.Alpha4))
            EnableKeyWord(4);
        else if (Input.GetKeyDown(KeyCode.Alpha5))
            EnableKeyWord(5);
        else if (Input.anyKeyDown)
            EnableKeyWord(-1); // Goto default functionality of sub-shader ( by disbaling all shader keywords )
    }

    private void EnableKeyWord(int index)
    {
        for (int i = 0; i < KeyWords.Length; i++)
        {
            if (i == index)
                Shader.EnableKeyword(KeyWords[i]);
            else
                Shader.DisableKeyword(KeyWords[i]);
        }
    }
}

Replacer.shader

Shader "BitshiftProgrammer/Replacer"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}

	SubShader
	{
		Tags { "RenderType"="Opaque" }

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma shader_feature UV_VIS
			#pragma shader_feature LOCAL_POS_VIS
			#pragma shader_feature WORLD_POS_VIS
			#pragma shader_feature DEPTH_VIS
			#pragma shader_feature LOCAL_NORMAL_VIS
			#pragma shader_feature WORLD_NORMAL_VIS
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
				float3 normal : NORMAL;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float3 worldPos : TEXCOORD1;
				float3 localPos : TEXCOORD2;
				float  depth : TEXCOORD3;
				float3 normal : TEXCOORD4;
				float4 vertex : SV_POSITION;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;
			
			v2f vert (appdata v)
			{
				v2f o;
				o.localPos = v.vertex;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.worldPos = mul(unity_ObjectToWorld, v.vertex);
				o.worldPos = normalize(o.worldPos);
				o.depth = -mul(UNITY_MATRIX_MV, v.vertex).z * _ProjectionParams.w;
				o.uv = v.uv;
				o.normal = v.normal;
				#if WORLD_NORMAL_VIS
				o.normal = mul(unity_ObjectToWorld, o.normal);
				#endif
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				#if UV_VIS
				return fixed4(i.uv, 0, 1);
				#endif
				#if LOCAL_POS_VIS
				return fixed4(i.localPos, 1.0);
				#endif
				#if WORLD_POS_VIS
				return fixed4(i.worldPos, 1.0);
				#endif
				#if DEPTH_VIS
				return i.depth;
				#endif
				#if LOCAL_NORMAL_VIS || WORLD_NORMAL_VIS
				return fixed4(normalize(i.normal) * 0.5 + 0.5,1.0);
				#endif
				return tex2D(_MainTex, i.uv); //If no shader feature is enabled
			}
			ENDCG
		}
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" "MyTag"="OnlyColors" }

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma shader_feature UV_VIS
			#pragma shader_feature LOCAL_POS_VIS
			#pragma shader_feature WORLD_POS_VIS
			#pragma shader_feature DEPTH_VIS
			#pragma shader_feature LOCAL_NORMAL_VIS
			#pragma shader_feature WORLD_NORMAL_VIS
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
			};

			struct v2f
			{
				float4 vertex : SV_POSITION;
			};

			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				return o;
			}

			fixed4 frag () : SV_Target
			{
				#if UV_VIS
				return fixed4(1,0,0,1);
				#endif
				#if LOCAL_POS_VIS
				return fixed4(0,1,0,1);
				#endif
				#if WORLD_POS_VIS
				return fixed4(0,0,1,1);
				#endif
				#if DEPTH_VIS
				return fixed4(1,1,0,1);
				#endif
				#if LOCAL_NORMAL_VIS
				return fixed4(1,0,1,1);
				#endif
				#if WORLD_NORMAL_VIS
				return fixed4(0,1,1,1);
				#endif
				return fixed4(1,1,1,1);
			}
			ENDCG
		}
	}
}

ShaderToBeReplacedWithTag.shader

Shader "BitshiftProgrammer/ShaderToBeReplacedWithTag"
{
	Properties 
	{
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}

	SubShader 
	{
		Cull off
		Tags { "RenderType"="Opaque" "MyTag"="OnlyColors" } // Tagged with "MyTag"

		CGPROGRAM
		#pragma surface surf Lambert noforwardadd

		sampler2D _MainTex;
		struct Input
		{
			float2 uv_MainTex;
		};

		void surf (Input IN, inout SurfaceOutput o)
		{
			fixed4 c = tex2D(_MainTex, IN.uv_MainTex);
			o.Albedo = c.rgb;
			o.Alpha = c.a;
		}
		ENDCG
	}
	Fallback "Mobile/VertexLit"
}