How to show a normal map on the INSIDE of a mesh: POSSIBLE?

I found the answer, it's rather straight forward. Might have looked more into this before asking. I found a unity page with shader examples (also with normals) here: https://docs.unity3d.com/Manual/SL-SurfaceShaderExamples.html

Just add a line (right after the Tags{} ) that says: 'Cull Front'.

 Shader "CUSTOM/NewImageEffectShader" 
 {
     Properties 
     {
         _MainTex ("Texture", 2D) = "white" {}
         _BumpMap ("Bumpmap", 2D) = "bump" {}
         _RimColor ("Rim Color", Color) = (0.26,0.19,0.16,0.0)
         _RimPower ("Rim Power", Range(0.5,8.0)) = 3.0
     }
 
     SubShader 
     {
         Tags { "RenderType" = "Opaque" }
 
         Cull Front
 
         CGPROGRAM
         #pragma surface surf Lambert
         struct Input 
         {
             float2 uv_MainTex;
             float2 uv_BumpMap;
             float3 viewDir;
         };
 
         sampler2D _MainTex;
         sampler2D _BumpMap;
         float4 _RimColor;
         float _RimPower;
 
         void surf (Input IN, inout SurfaceOutput o) 
         {
             o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
             o.Normal = UnpackNormal (tex2D (_BumpMap, IN.uv_BumpMap));
             half rim = 1.0 - saturate(dot (normalize(IN.viewDir), o.Normal));
             o.Emission = _RimColor.rgb * pow (rim, _RimPower);
         }
 
         ENDCG
     }
 
     Fallback "Diffuse"
 }