I have an office that I'm thinking of closing down and moving back to my apartment. Will my apartment then be considered (by NYC) a "commercial" space and thus have a commercial lease?. or can I continue with my present lease which is a "residential" lease)?

1. will you be allowed to even have a business there. If this is not zoned for your type of business you can't even do it.

2. you can not merely change your current lease without permission of the landlord

3. they may be , normally will be a clause that no business can be ran from this.

And of course what type of office, will there be customers coming to your location, or is it merely a office for a outside business that never has customers coming to your location

Yeah, you have to speak to the landlord... mine specifically said we cannot run ANY type of business out of the apartment, I never really asked why but I'm sure it's for insurance reasons.