What is the process of switching a US-registered fictitious business name from an Inc ran by one individual to an Independent Contractor?
This question is based around the Inc deing dissolved, the business name already registered with the IRS, and the fictitious name having no "Inc." or business entity added in it.
You would need to:
Contact your state and find out if you can reregister the name as a different entity type (most of the time, it's a matter of proving you used to own the inc)
Contact IRS and get a new EIN for the new entity type (you may be able to keep the same one if you're going from inc to LLC-treated as corp, although that defeats a purpose of de-incing normally)
Switch over all your accounts, vendors, etc to the new entity
Now that said I would not suggest just doing sole proprietorship (i take it that's what you're looking at as you said no entity attached to the name). Reason being, sole proprietership means anything that happens, happens to you. LLC is a much better way, costs are a few hundred a year, taxes are normally filed on personal returns, however you're protected as a corp.