Unlit Transparent Cutout shader that can switch between two textures

Hi all,

I've been doing a bit of research into shaders (which I am brand new to, btw), as I would like a shader that is essentially the same as Unity's built in Unlit Transparent Cutout shader, but will render one of two textures based on a property that I can set through code. Here is what I have so far (which is basically all taken from the built in shader):

 Shader "Example/Unlit Transparent Cutout Test" {
 Properties {
     _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
     _SecondTex ("Base (RGB) Trans (A)", 2D) = "white" {}
     _TexValue ("Texture Value", Range(0,1)) = 0.0
 }
 
 SubShader {
     Tags {"Queue"="AlphaTest" "IgnoreProjector"="True" "RenderType"="TransparentCutout"}
     LOD 100
     
     Pass {
         Lighting Off
         Alphatest Greater [_Cutoff]
         SetTexture [_MainTex] { combine texture } 
     }
 }
 }

I'm guessing that I have to change something in the SetTexture part, but I'm not sure what. Any help would be much appreciated. Thanks!