Please keep in mind, that with this very simple configuration, only the link types will be updated. The updated_at date of the product entity itself will NOT be refreshed. If this is o. k. for you, have fun :-)

Step 1: Configuration

Create a configuration snippet <magento-install-dir>/app/etc/configuration/operations.json with the content

{
	"operations": {
		"ce": {
			"catalog_product": {
				"links": {
					"plugins": {
						"subject": {
							"id": "import.plugin.subject",
							"subjects": [{
								"id": "import_product.subject.bunch",
								"file-resolver": {
									"prefix": "product-import"
								},
								"params": {
									"clean-up-empty-columns": []
								},
								"observers": [{
									"import": [
										"import_product.observer.last.entity.id", 
										"import_product_link.observer.product.link", 
										"import_product.observer.clean.up"
									]
								}]
							}]
						}
					}
				}
			}
		}
	}
}

Additionally, we need to create a second configuration snippet <magento-install-dir>/app/etc/configuration/shortcuts.json with the content

{
	"shortcuts": {
		"ce": {
			"catalog_product": {
				"links": [
					"general/general/global-data",
					"general/general/move-files",
					"general/catalog_product/collect-data",
					"ce/catalog_product/links", 
				    "ce/catalog_product/add-update.links"
				]
			}
		}
	}
}

Step 2: CSV Structure

In the second step, we've a look at the structure of the CSV file that contains the product status data. As explained at the start of the post, we only want to update the link types. This makes thinks very easy, as the CSV file MUST have at least two columns, namely SKU and <link-type>_skus. The file, for example, will then look like this

sku
related_skus
24-MB01
24-MB05,24-MB03,24-MB04
24-MB04
24-MB05,24-MB03,24-MB02
24-MB03
24-MB05,24-MB01,24-MB04

Step 3: Execute the command

Finally, copy the CSV file(s),with the structure above to the directory <magento-install-dir>/var/importexport and execute the command which updates the link types

<magento-install-dir>/bin/import-cli-simple.phar import:create:ok-file \     
  && <magento-install-dir>/bin/import-cli-simple.phar import:products links

Done!