So, after I discovered something about the chain of command that I had not noticed before, I asked an admin about this: "The HoP can fire and reassign people with other head's consent, can assign people freely, and can substitute the role of another head of staff in their absence, excluding Head of Security."
I really do not understand that, the admin explained me these points:
Well then. WALLS OF TEXT AHEAD, THAT'S WHY I USED SPOILERS
Phew, all this just to say: "I want the Head of Personnel to be able to substitute the HoS if he is missing because I don't believe the HoS is any different from any head of the staff". And the reasoning behind is: "The Head of Personnel, while substituting the Head of Security, would do as a captain with no knowledge of field combat would do, commanding and instructing orders instead of getting into a fight" and I may add: "If there was no captain, but there was a head of security, the Head of Personnel would take the Captain's place and become acting captain, where he would command and instruct orders to the security staff and not get involved in the actual procedure"
So, that's that. I'd say an acting HoS would work the same as any other acting Head of the Staff, I don't see no difference in their work except for the fields of knowledge, of course.