Rewrite shader so that the Sprite-Diffuse shader doesn't take incidence angle into consideration when applying lighting?

Solved it.

You can actually override Unity lighting!

Code that does what I want:

 Shader "Sprites/DiffusePoint"
 {
     Properties
     {
         [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
         _Color ("Tint", Color) = (1,1,1,1)
         [MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
     }
 
     SubShader
     {
         Tags
         { 
             "Queue"="Transparent" 
             "IgnoreProjector"="True" 
             "RenderType"="Transparent" 
             "PreviewType"="Plane"
             "CanUseSpriteAtlas"="True"
         }
 
         Cull Off
         Lighting Off
         ZWrite Off
         Blend One OneMinusSrcAlpha
 
         CGPROGRAM
         #pragma surface surf PointLambert vertex:vert nofog keepalpha
         #pragma multi_compile _ PIXELSNAP_ON
         #pragma shader_feature ETC1_EXTERNAL_ALPHA
 
         sampler2D _MainTex;
         fixed4 _Color;
         sampler2D _AlphaTex;
 
         half4 LightingPointLambert(SurfaceOutput s, half3 lightDir, half atten) {
             half4 c;
             c.rgb = s.Albedo * _LightColor0.rgb * atten;
             c.a = s.Alpha;
             return c;
         }
 
         struct Input
         {
             float2 uv_MainTex;
             fixed4 color;
         };
         
         void vert (inout appdata_full v, out Input o)
         {
             #if defined(PIXELSNAP_ON)
             v.vertex = UnityPixelSnap (v.vertex);
             #endif
             
             UNITY_INITIALIZE_OUTPUT(Input, o);
             o.color = v.color * _Color;
         }
 
         fixed4 SampleSpriteTexture (float2 uv)
         {
             fixed4 color = tex2D (_MainTex, uv);
 
 #if ETC1_EXTERNAL_ALPHA
             color.a = tex2D (_AlphaTex, uv).r;
 #endif //ETC1_EXTERNAL_ALPHA
 
             return color;
         }
 
         void surf (Input IN, inout SurfaceOutput o)
         {
             fixed4 c = SampleSpriteTexture (IN.uv_MainTex) * IN.color;
             o.Albedo = c.rgb * c.a;
             o.Alpha = c.a;
         }
         ENDCG
     }
 
 Fallback "Transparent/VertexLit"
 }