The d tag is the unique identifier and cannot be updated. If a client will integrate an 'update bookmark' feature, that will mean a new event will be created with a new identifier. Then it's up to a client to do some matching for whatever reason.
Discussion
Maybe two kind is the best solution
simple link 39700 (without changing the spec) like https://github.com/symfony/symfony/
category link 39701 like https://github.com/symfony/symfony/blob/7.2/src/Symfony/Component/HttpFoundation/Request.php#L98