Modify texture coordenates with a shader.

I have a TextureAtlas with 4x4 tiles managed by a shader. I need a margin to avoid the texture bleeding produced by mipmaps.

Does anyone know how to subtract an uv offset from the final tile region?

 Shader "TileableAtlas 4x4" {
 
     Properties {
         _MainTex ("Base (RGB)", 2D) = "white" {}
     }
     SubShader {
         Tags { "RenderType"="Opaque" "IgnoreProjector" = "True"}
         LOD 200
        
         CGPROGRAM
         #pragma exclude_renderers gles
         #pragma debug
         #pragma surface surf Lambert
         #pragma vertex vert
         #include "UnityCG.cginc"
  
         sampler2D _MainTex; 
 
       struct Input {
             float2 uv_MainTex;
             float4 color: Color; // Vertex color
         };
 
       struct appdata {
         float4 vertex : POSITION;
             float4 texcoord : TEXCOORD0;
                 fixed4 color : COLOR;
         };
 
         void vert (inout appdata_full v) {        }
  
         void surf (Input IN, inout SurfaceOutput o) { 
 
         half4 c = tex2D(_MainTex, (frac(IN.uv_MainTex) * 0.25f) + float2(IN.color.r,IN.color.g));
        o.Albedo = c.rgb;
         }
         ENDCG
     }
     FallBack "Diffuse"
 }