Material.Lerp for transparent spec material with two different textures

Here's a shader that will do that...

 Shader "Whydoidoit/Lerp" {
 
     Properties {
     
         _MainTex ("First Texture", 2D) = "white" {}
         _BlendTex ("Second Texture", 2D) = "white" {}
         _Blend ("Blend", Range(0,1)) = 0.0
     
     }
     
     SubShader {
         Tags {"RenderType"="Opaque"}
         LOD 200
         CGPROGRAM
         #pragma surface surf Lambert
         
         sampler2D _MainTex;
         sampler2D _BlendTex;
         float _Blend;
         
         struct Input {
             float2 uv_MainTex;
             float2 uv_BlendTex;
         };
         
         
         void surf(Input IN, inout SurfaceOutput o) {
             
             half4 c1 = tex2D(_MainTex, IN.uv_MainTex);
             half4 c2 = tex2D(_BlendTex, IN.uv_BlendTex);
             o.Albedo = (c1.rgb * (1-_Blend)) + (c2.rgb * _Blend); 
             o.Alpha = 1;
         
         }
         
         ENDCG
         
     }
     Fallback "Diffuse"
 
 }

@ina,

I don't believe so, but I haven't specifically tried it. Most likely you'd want to write a custom shader that uses two textures and a float value to sample both of them. This is very hard to do if you've never written a shader, but if you want to try it, check out this page: http://docs.unity3d.com/Documentation/Components/SL-SetTexture.html

There's an example there (Alpha Blending Two Textures) that might just do what you want.