Yes you can top the very top grow tip of your plant, but I would take the tip and maybe 1 or 2 lower set of leaves. Take about an inch of the top and clone it. Just make sure you have enough stalk to set in your rapid rooter, or rock wool. Dont use the jiffy pellets, they are not pH neutral so they'll hamper your clone taking root. The longer the top the better to clone. After vegging for 30 days, and sexing your plant under 12/12 lighting, you should be able to clone some of the bottom branches leaving the very top to produce your cola. Once you know you're cloning a female you can increase the length of light back and veg some more. The longer your plant can veg the bigger your harvest. Hope this helps
Nim