I think it is oh so much easier.
If I install any new wiring, at any point in a new circuit, that new wiring must meet todays codes.
That would mean it must be AFCI protected.
It blows my mind that people think they can avoid the new rules just because they choose to use an existing circuit in some way.
I wanted to use this:
"102.6 Existing structures.
The provisions of Section 115 shall control the alteration, repair, addition and change of occupancy of any existing structure.
The occupancy of any structure currently existing on the date of adoption of this code shall be permitted to continue without change, provided the alleged occupancy can be shown to have existed and there are no orders of the building official pending, no evidence of fraud or no serious safety or sanitation hazard.
Buildings constructed in accordance with plans which have been approved prior to the effective date of this code are existing buildings."
But this applies:
"115.4 Additions and alterations.
Additions or alterations to residential buildings shall conform to the requirements of the code for new construction and shall be approved by the residential building official. Additions or alterations shall not be made to an existing building or structure which will cause the existing building or structure to be in violation of any provisions of this code. Except as otherwise provided for in Section R313.1.1, portions of the structure not altered and not affected by the alteration are not required to comply with the code requirements for a new structure."
"115.5 Alterations to systems, components and materials.
Alterations to an existing system (egress, fire protection, mechanical, plumbing, etc.) and materials or building components not otherwise provided for in this section shall conform to that required for new construction to the extent of the alteration. The existing systems, materials or components shall not be required to comply with all of the requirements of this code for new construction except to the extent that they are affected by the alteration. Additions or alterations to existing systems materials or components shall not cause them to become unsafe, hazardous, overloaded or become less effective than when originally installed, constructed and/or approved."
The new wire must be AFCI protected (where required under 210.12) not the rest of the circuit. Do you like that statement?
So I agree with Bob.