Custom transmission texture in Unity

LegacyTransparencyLM.shader

Shader "Transparent/Transmission"
{
    Properties
    {
    	_Color ("Main Color", Color) = (1,1,1,1)
    	_MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
    	_TransparencyLM("Transmission", 2D) = "white" {}
    }

    SubShader
    {
    	Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" }

        CGPROGRAM
        #pragma surface surf Lambert alpha

        sampler2D _MainTex;
        fixed4 _Color;

        struct Input
        {
        	float2 uv_MainTex;
        };

        void surf (Input IN, inout SurfaceOutput o)
        {
        	fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
        	o.Albedo = c.rgb;
        	o.Alpha = c.a;
        }
        ENDCG
    }

    Fallback "Transparent/VertexLit"
}