so i have

var itemInfo = ItemManager.FindItemDefinition("hat.cap");
var crownMod = itemInfo.GetOrAddComponent<theCrown>();
Item crown = ItemManager.Create(itemInfo, 1, 839691853);​

     public class theCrown : ItemMod
     {
          public Item crown;
          public string name = "The Crown2";

          public override void ModInit()
          {
               instance.Puts("Init");
          }
}

I can make a call to the ModInit on creation but should it no be making the call when the item inits?

I believe you should add it to mods array of item definition also, don't remember but might cause issues. And there is on item created or something similar.

how do i add to the array? i got lost trying i tryed with itemdef.itemMods.Add said does not contain a def for Add

The following plugin on the first page of recent plugins does something like this.
https://umod.org/plugins/general-item-modifier