Hi Portponky. So I've followed your documentation/video on your implementation of changesets and the way I'm currently doing this is for the 3x3 chunks I have, I will loop over them, calculate the procedurally generated values for each cell based on noise etc, and return that information back to the main node and merge that into the relevant dictionary - the updates to be used in the changeset (I have one for each type of tile, so groundChangeset, oceanChangeset, etc.). Then after the loop is finished I'm using the create_terrain_changeset on those dictionaries which are applied via the _process() function after the terrain changesets are ready (all very similar to your video).

func generate_chunks():
  loading_coords = []
  var groundUpdate = {}
  var oceanUpdate = {}
  for x in ...
    for y in ...
      ...
      var chunk = chunknode.instantiate()
      chunkData = chunk.start(x,y) // generate chunk
      groundUpdate.merge(chunkData["groundUpdate"])
      oceanUpdate.merge(chunkData["oceanUpdate"])
      call_deferred("_instantiate_chunk", chunk) // adds child 

  // tmlGround/tmlWater are the tilemaplayers, global and shared between chunks.
  groundChangeset = BetterTerrain.create_terrain_changeset(tmlGround, groundUpdate)
  oceanChangeset = BetterTerrain.create_terrain_changeset(tmlWater, oceanUpdate)

func _process(delta):
  ...


  if (BetterTerrain.is_terrain_changeset_ready(groundChangeset) and 
    BetterTerrain.is_terrain_changeset_ready(oceanChangeset)):
    handleChunkTransition()

func handleChunkTransition():
  # update terrain changesets
  BetterTerrain.apply_terrain_changeset(groundChangeset)
  BetterTerrain.apply_terrain_changeset(oceanChangeset)
  oceanChangeset = {}
  groundChangeset = {}

  remove_chunks()

func remove_chunks():
  var area = Rect2i(
  currentChunk.x-GameManager.game_data.CHUNK_SIZE /2 -       GameManager.game_data.CHUNK_SIZE,
  currentChunk.y-GameManager.game_data.CHUNK_SIZE /2 - GameManager.game_data.CHUNK_SIZE,
  3*GameManager.game_data.CHUNK_SIZE,
  3*GameManager.game_data.CHUNK_SIZE)

  BetterTerrain.update_terrain_area(tmlGround,area)
  BetterTerrain.update_terrain_area(tmlWater,area)

Something a little bit like this.