I honestly don't know how this isn't a thing already, maybe I missed it on the wiki, but without any resource to say what the ids for skills are the command to bind actions to the 2 quick use keys is unusable. All the book, the help command, and the skills page on the wiki say to do is just type "action-id" as if i know what to type there. I've been sitting here for 5 minutes trying to just guess the id for the dark blood projectile because like, what else am I expected to do?
Edit: I found that the wiki does say to use autocomplete to see the ids, except...that doesn't work. Autocomplete isn't showing up for this command when I use it. I guess that makes this a bug, then? I don't know.

If you are using minecraft 1.14+ that is possible with /vampirism bind-action <1,2> and then the action ids should be shown. (1 or 2 depending on the quick button). It is also possible to press 1 or 2 when selecting an action in the action menu.
Not sure about 1.12

I have added a list of actions to the "help" subcommand of "bind-action" in the latest 1.15 version.
However, the autocomplete should work well for 1.14+.
1.12 might be worse, but isn't supported anymore.

Here is an up-to-date list