I am not knowledgeable enough to know, but would drilling into a lithium cell possibly be hazardous?
Yes, yes it will. You should never puncture a battery.
Edit:
Never ever!
Could you possibly get away with it and have people probably done it before? Yes and yes.
Can you hurt yourself doing it? YES
I have seen people come through our ER with battery related injuries. Whoever is telling you to drill into a battery should also agree to pay your hospital bills if it goes bad...
Lol. Send me the bill.