There are a number of tag groups where the tags are different but there is also another "parent" tag that is correct for all, like 2girls/boys & 3girls/boys, etc. with the multiple_girls/boys tag or double_penetration & triple_penetration with the multiple_penetration "parent" tag.

Is it possible that those "parent" tags are automatically added for at least some of those tag groups? Or would that require to extend the api or something?

We have a bot running in the background that examines tag edits/ uploads and adds implications automatically.

We keep a list of these implications here: gelbooru.com/index.php?page=tags&s=implications