I don't rename it, I release a new updated dataset. However, each dataset is a superset of the previous one, so you can always reconstruct the old one and thus 'Danbooru2018', 'Danbooru2019', 'Danbooru2020', 'Danbooru2021' etc have exact well-defined meanings that never change, and if you don't happen to have a copy of Danbooru2018 sitting around, you can just download Danbooru2021, unpack the Danbooru2018 metadata from the archive tarball & delete the post-Danbooru2018 images, and you now have a bit-for-bit copy of Danbooru2018.

Also, if you want to just discuss the general concept of boorus (there are many beyond Danbooru), it'd probably be better to invoke Safebooru https://safebooru.org/ which is what it sounds like.