Something I wasn't sure about during our first Pegasus game with a Cylon Leader - is it possible for the Cylon Leader to activate the Human Fleet location to infiltrate before Galactica has returned and if so where do you place them on the board.

My first thought is that since the Human Fleet location says that you infiltrate Galactica, you cannot utilize the space until after Galactica has returned, but that means that if the Cylon Leader isn't infiltrating then they are stuck as a Cylon on New Caprica for pretty much the entire NC phase, which makes them almost useless, if they have a sympathetic agenda.

Yeah, you got it. If they can infiltrate before the NC Phase, they can keep going, but you can't start an infiltration without the Human Fleet location, which is off limits until Galactica returns.

Any official answers to the infiltrating leaders on Caprica?

I see 4 possible options:

A) It is not possible to infiltrate here. the leader must stop its infiltration and can only infiltrate again after Galactica returns.

B) It is not possible to start an infiltration here. If you have infiltrated before New Caprica phase, you can continue. Otherwise you must act like a cylon until Galactica returns.

C) It is not possible to end an infiltration here. You must continue infiltrating here and can only revert back when Galactica returns. You can however start an infiltration here (question is of course: how?).

D) It is not possible to change mode here. The leader must continue the mode he had when the New Caprica phase began. He can only change mode when galactica returns.

It is very easy for a cylon leader to be infiltrating on NC. You must simply be infiltrating before that phase. You are then treated as a human player and all human players are placed at the resistance HQ when New caprica shows up. It is pretty simple for the humans to kick you out and make you a cylon instead by using the resistance HQ action to execute you. You cannot enter infiltration until Galactica shows back up, as said before.