New :

A new config file "entity-type-that-should-spawn-head_config.json" allows you to list custom entity types that can spawn skulls and respawn as the original entity :

{
  "skeletonHeadEntities": [
    "minecraft:skeleton",
    "modid:custom_archer"
  ],
  "witherSkeletonHeadEntities": [
    "minecraft:wither_skeleton",
    "modid:dark_knight"
  ]
}