How to add person's name in existing booking?

[lets_party]

OK here is dealio:

Two of us have booked our trip already (all inclusive).

One of my other friend wants to come.

He said that he will book his flight seperatly (he is flying from another town), but I will need to add his name to the hotel.

I called cheaptickets.com (we booked our flight through them), they called hotel (Oasis) and cheapticket rep told me that I can add my friend for $50 per night including tax. My friend will need to pay that price upon check in.

However, cheapticket stafff haven't given me any written confirmation about this. Obviously price is unbeatable, but it would be nice to have some sort of confirmation.

So in nutshell, I want to add my friend's name in our existing hotel reservation (same room). What is best way to do this apart from him booking the room on the day of checkin? OR Is there direct email to Oasis or GrandOasis staff where I can get some sort of confirmation via email?