Shader Decal - Multiply / Add not simple blend by alpha

Hi, i'm using this simple Unlit decal shader.

  Properties {
       _Color ("Main Color", Color) = (1, 1, 1, 1)
       _MainTex ("Base (RGB)", 2D) = "white" {}
       _DecalTex ("Decal (RGBA)", 2D) = "black" {}
    }
    
    SubShader {
    
       Tags {
          "Queue"="Transparent"
          "IgnoreProjector"="True"
          "RenderType"="Transparent"
       }
      
       Pass {
        
          BindChannels {
             Bind "Vertex", vertex
             Bind "normal", normal
             Bind "texcoord", texcoord0 // main uses 1st uv
             Bind "texcoord1", texcoord1  // decal uses 2nd uv
          }
          
 
        
          SetTexture [_MainTex] {
             constantColor [_Color]
             Combine texture * constant
          }
          
          SetTexture [_DecalTex] {
             combine texture lerp (texture ) previous
          }
 
       }
       
    }

How can i add or multiply the decal to the maintexture? Someone? Thanks in advance!