Transparent Terrain Texture Painting (3.5 Free version)

Ok hallo everyone , first of all i dont know anything about shaders and i am not keen into start learning but i need them for first and last time for my game , i want to paint parts of my terrain or the whole terrain trasparent ( not tottaly invisible but a bit ) and i came into this outdated script , i tried to fix it but with no luck any help ? this is the script : Shader "Nature/Terrain/Diffuse" { Properties { _Control ("Control (RGBA)", 2D) = "red" {} _Splat3 ("Layer 3 (A)", 2D) = "white" {} _Splat2 ("Layer 2 (B)", 2D) = "white" {} _Splat1 ("Layer 1 (G)", 2D) = "white" {} _Splat0 ("Layer 0 (R)", 2D) = "white" {} //Used in fallback on old cards & base map _MainTex ("BaseMap (RGB)", 2D) = "white" {} _Color ("Main Color", Color) = (1,1,1,1) }

     SubShader
     {
         Tags
         {
             "SplatCount" = "4"
             "Queue" = "Geometry-100"
             "RenderType" = "Opaque"
         }
         Blend SrcAlpha OneMinusSrcAlpha
         
         CGPROGRAM
         #pragma surface surf Lambert
         struct Input
         {
             float2 uv_Control : TEXCOORD0;
             float2 uv_Splat0 : TEXCOORD1;
             float2 uv_Splat1 : TEXCOORD2;
             float2 uv_Splat2 : TEXCOORD3;
             float2 uv_Splat3 : TEXCOORD4;
         };
  
         sampler2D _Control;
         sampler2D _Splat0,_Splat1,_Splat2,_Splat3;
  
         void surf (Input IN, inout SurfaceOutput o)
         {
             fixed4 splat_control = tex2D (_Control, IN.uv_Control);
             fixed4 firstSplat = tex2D (_Splat0, IN.uv_Splat0);
             fixed3 col;
             col = splat_control.r * tex2D (_Splat0, IN.uv_Splat0).rgb;
             col += splat_control.g * tex2D (_Splat1, IN.uv_Splat1).rgb;
             col += splat_control.b * tex2D (_Splat2, IN.uv_Splat2).rgb;
             col += splat_control.a * tex2D (_Splat3, IN.uv_Splat3).rgb;
             o.Albedo = col;
             o.Alpha = 1;
             if(tex2D(_Splat0, IN.uv_Splat0).a == 0)
                 o.Alpha = 1 - splat_control.r;
             else if(tex2D(_Splat1, IN.uv_Splat1).a == 0)
                 o.Alpha = 1 - splat_control.g;
             else if(tex2D(_Splat2, IN.uv_Splat2).a == 0)
                 o.Alpha = 1 - splat_control.b;
             else if(tex2D(_Splat3, IN.uv_Splat3).a == 0)
                 o.Alpha = 1 - splat_control.a;
         }
         ENDCG
     }
  
     Dependency "AddPassShader" = "Hidden/TerrainEngine/Splatmap/Lightmap-AddPass"
     Dependency "BaseMapShader" = "Diffuse"
  
     //Fallback to Diffuse
     Fallback "Diffuse"
 }

and the errors are these : Shader warning in 'Nature/Terrain/Diffuse': Not enough temporary registers, needs 9 (compiling for flash) at line 25 Shader warning in 'Nature/Terrain/Diffuse': Not enough temporary registers, needs 10 (compiling for flash) at line 25

can anyone fix them , cause i have no idea