簡易的な例

resource "null_resource" "hogehoge" {
  triggers = {
    fugafuga = "fugafuga" // ここが変わると直下に記載してあるlocal-execが実行される（whenが指定されてない方）
  }
  provisioner "local-exec" {
    interpreter = ["ruby", "-e"]
    command     = "puts 'hogefuga'"
  }
  provisioner "local-exec" {
    interpreter = ["ruby", "-e"]
    command     = "puts 'fugapiyo'"
    when        = destroy // こっちは削除時に実行される（whenで指定してあるため）
  }
}

具体例

resource "google_bigquery_dataset" "shared_udf" {
  dataset_id = "shared_udf"
  location   = local.japan_tokyo_region
}

locals {
  japan_tokyo_region = "asia-northeast1"
  udfs = {
    example : <<EOF
CREATE OR REPLACE FUNCTION ${google_bigquery_dataset.shared_udf.dataset_id}.example(x INT64)
RETURNS INT64
  LANGUAGE js AS """
  return x*2;
""";
EOF
  }

}

resource "null_resource" "udfs" {
  for_each = local.udfs
  triggers = {
    udf = each.value
    project_id = var.project_id
    location = local.japan_tokyo_region
    udf_dataset_id = google_bigquery_dataset.shared_udf.dataset_id // destroy時のwarningへの暫定対応 望ましくないがとりあえず https://github.com/hashicorp/terraform/issues/23679
  }
  provisioner "local-exec" {
    interpreter = ["bq", "query", "--use_legacy_sql=false", "--project_id=${self.triggers.project_id}", "--location=${self.triggers.location}"]
    command     = each.value
  }
  provisioner "local-exec" {
    interpreter = ["bq", "query", "--use_legacy_sql=false", "--project_id=${self.triggers.project_id}", "--location=${self.triggers.location}"]
    command     = "DROP FUNCTION IF EXISTS ${self.triggers.udf_dataset_id}.${each.key}"
    when        = destroy
  }
}

参考