Combining a custom shader with a normal one

Hello, I wanted to ask if it is possible to combine the following two shaders in Unity:

1. A custom Vertexcolor shader I made so that I could import vertexpainted models from Blender

2. The Unity Toon shader

I want to combine them because the Vertexcolor shader does not react to light, which is a big problem since my game is heavily based on lighting.

Here's the script for my custom shader:

 Shader "Custom/Vertexcolors" {
     Properties {
     }
     SubShader {
         Pass {
         CGPROGRAM
         #pragma vertex vert
         #pragma fragment frag
 
         struct vertexInput {
             float4 vertex : POSITION;
             float4 color : COLOR;
         };
 
         struct vertexOutput {
             float4 pos : SV_POSITION;
             float4 vertCol: COLOR;
         };
 
         vertexOutput vert(vertexInput v){
             vertexOutput o;
             o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
             o.vertCol = v.color;
             return o;
         }
         
         float4 frag(vertexOutput i) : COLOR
         {
             return i.vertCol;
         }
         ENDCG
         }
     } 
     //FallBack "Diffuse"
 }