How to write Diffuse shader with Pass{} instead of surface?

You can set Cull Front and Cull Back using surface shaders...

 Shader "Custom/DoubleSided" {
 Properties {
 _MainTex ("Base (RGB)", 2D) = "white" {}
 }
 SubShader {
 Tags { "RenderType"="Opaque" }
 LOD 200
  
 // Render back faces first
 Cull Front
 CGPROGRAM
 #pragma surface surf Lambert vertex:vert
  
 sampler2D _MainTex;
  
 struct Input {
 float2 uv_MainTex;
 };
  
 // Flip normal for back faces
 void vert (inout appdata_full v) {
 v.normal *= -1;
 }
  
 // Red back faces
 void surf (Input IN, inout SurfaceOutput o) {
 half4 c = tex2D (_MainTex, IN.uv_MainTex);
 o.Albedo = fixed3(1,0,0);
 o.Alpha = c.a;
 }
 ENDCG
  
 // Now render front faces
 Cull Back
 CGPROGRAM
 #pragma surface surf Lambert
  
 sampler2D _MainTex;
  
 struct Input {
 float2 uv_MainTex;
 };
  
 // Green front faces
 void surf (Input IN, inout SurfaceOutput o) {
 half4 c = tex2D (_MainTex, IN.uv_MainTex);
 o.Albedo = fixed3(0,1,0);
 o.Alpha = c.a;
 }
 ENDCG
  
  
 }
 FallBack "Diffuse"
 }