I apologize in advance for my lack of knowledge. In my basement I currently have a single 20A circuit with 6 lights on it, rated at 150W each, controlled by a single light switch. I'd like to know if its possible to break these lights up without adding circuits. Is it as simple as adding a switch in between the lights? Will the lights further down the line stay hot when the first switch is off? Again, I apologize for my lack of knowledge and any help would be greatly appreciated. Thanks.

It will be in all how you connect the wires, if the new switch is fed by the existing switch, then all the lights are controlled by one switch. If you feed the new switch with constant power, then each switch will control it's own bank of lights.

NO... hire and electrician... sounds like you need the code of city before this challenged... get it right the first time... call a Union