Since with version 3.8.0 it is no longer necessary to overwrite the complete configuration file, but only the affected configurations, it is sufficient to create a corresponding snippet, e. g. <magento-install-dir>/app/etc/configuration/operations.json, which has the following content


	"operations": {
		"ce": {
			"catalog_product": {
				"validate": {
					"plugins": {
						"subject": {
							"id": "import.plugin.subject",
							"listeners": [{
								"plugin.process.start": [
									"import.listener.reset.loader.eav.attribute.option.value"
								],
								"plugin.process.success": [
									"import.listener.stop.validation"
								]
							}],
							"subjects": [{
								"id": "import.subject.validator",
								"create-imported-file": false,
								"date-converter": {
									"source-date-format": "d.m.y, H:i"
								},
								"file-resolver": {
									"prefix": "product-import"
								},
								"listeners": [{
									"subject.artefact.header.row.process.start": [
										"import.listener.validate.header.row"
									]
								}],
								"params": {
									"custom-validations": {
										"sku": ["/.+/"],
										"product_type": [
											"simple", 
											"virtual", 
											"configurable", 
											"bundle", 
											"grouped", 
											"giftcard"
										],
										"visibility": [
											"Not Visible Individually", 
											"Catalog", 
											"Search", 
											"Catalog, Search"
										]
									}
								},
								"observers": [{
									"import": [
										"import_product.observer.composite.base.validate"
									]
								}],
								"callbacks": [{
									"sku": ["import.callback.custom.regex.validator"],
									"store_view_code": ["import.callback.store.view.code.validator"],
									"attribute_set_code": ["import.callback.attribute.set.name.validator"],
									"product_type": ["import.callback.custom.array.validator"],
									"tax_class_id": ["import_product.callback.validator.tax.class"],
									"product_websites": ["import.callback.store.website.validator"],
									"visibility": ["import.callback.visibility.validator"],
									"related_skus": ["import_product.callback.validator.link"],
									"upsell_skus": ["import_product.callback.validator.link"],
									"crosssell_skus": ["import_product.callback.validator.link"],
									"created_at": ["import.callback.validator.datetime"],
									"updated_at": ["import.callback.validator.datetime"],
									"special_price_to_date": ["import.callback.validator.datetime"],
									"special_price_from_date": ["import.callback.validator.datetime"],
									"custom_design_to": ["import.callback.validator.datetime"],
									"custom_design_from": ["import.callback.validator.datetime"],
									"new_to_date": ["import.callback.validator.datetime"],
									"new_from_date": ["import.callback.validator.datetime"],
									"price": ["import.callback.validator.number"],
									"special_price": ["import.callback.validator.number"],
									"map_price": ["import.callback.validator.number"],
									"msrp_price": ["import.callback.validator.number"],
									"qty": ["import.callback.validator.number"]
								}]
							}]
						}
					}
				}
			}
		},
		"ce": {
			"catalog_product": {
				"add-update": {
					"plugins": {
						"subject": {
							"id": "import.plugin.subject",
							"subjects": [{
								"id": "import_product.subject.bunch",
								"date-converter": {
									"source-date-format": "d.m.y, H:i"
								},
								"file-resolver": {
									"prefix": "product-import"
								},
								"params": {
									"copy-images": false,
									"clean-up-media-gallery": true,
									"clean-up-empty-image-columns": true,
									"clean-up-website-product-relations": true,
									"clean-up-category-product-relations": true,
									"clean-up-empty-columns": [
										"special_price",
										"special_price_from_date",
										"special_price_to_date"
									]
								},
								"observers": [{
									"import": [
										"import_product.observer.composite.base.add_update"
									]
								}]
							}]
						}
					}
				}
			}
		}
	}
}

In the example above, we override the validation as well as the add-update operation, as both need the appropriate date format. As this changed the date format to d.m.y, H:i, the file MUST contain dates like 17.01.20, 14:11.