no. Most people top a plant to provide more bud sites and at 5 weeks, it's too late for that.
Yes, you can absolutely harvest the top and let the rest grow but be aware that if the plant is matured the stuff not getting light could very well just never develop or be over ripe by the time it does. With a dwarf, you are usually only growing the 1 main cola anyway though. Got a pic? What are u using for light?