How do I combine two actions into one?

I have two actions, one creates a user the other one invites a user, I want to combine them into a single one, so when a user gets created, they get invited right away too. Is it possible? I know I about the after hook but I don't know how to execute an action from there. One important thing to note is that both actions are from plugins so it wouldn't be nice to extract the code from the packages.