How can I add a field to an Enum?

[untold-titan]

I'm trying to write a mod for a unity game, and I'm using cecil to edit the main assembly of the game.

This is the code I'm using:

var module = assembly.MainModule;
var itemType = module.GetType("EItemType");

var TestInjectedItem = new FieldDefinition("InjectedItem", FieldAttributes.Public | FieldAttributes.Static | FieldAttributes.Literal, itemType) { Constant = 114 };
itemType.Fields.Add(TestInjectedItem);

// Overwrite the assembly in the game files hehehe
assembly.Write();

I have double checked using dotPeek to make sure that 114 is a valid constant value (eg incrementing the previous ones)

This is the class I'm editing:

public enum EItemType
{
  None = -1, 
  BasicCardPack = 0,
  BasicCardBox = 1,
//...
  PlayMat16 = 110, 
  PlayMat17 = 111,
  PlayMat18 = 112, 
  Max = 113,
}