How to define dynamically / override the _default_ mapping in elasticsearch?

Use case :

1. The index/indices will be built dynamically from a template, so that it will pick some custom settings (number of shards/replicas/ etc).

2. Generate dynamically the types and their mappings, enabling for them all the timestamp & ttl fields. Also define the same parent type for all types, except the parent type itself (I know its name).

   {
      "template": "*",
   
      "settings": {
         ...................
      },
   
      "mappings": {
   
         "_default_": {
            "_parent": {
               "type": "ParentType"
            },
            "_timestamp": {
               "enabled": true,
               "store": true
            },
            "_ttl": {
               "enabled": true
            }
         }
   
      }
   }
   

How could I disable the _parent field for the ParentType type itself ?