This is a highly unkown code, even though it represents law in New Jersey. Knowing the codes is extremely important when making home repairs of any kind. Its even more important when repairing a chimney.
Commonly, I will see repairs being done by chimney contractors that are not compliant with the codes. The rehab code is actually very clear and is not open to interpretation. Under the section "repairs" it states that repairs must follow "approved materials and methods" as outlined in the section. Those materials and methods reference the New Jersey Residential Code 2006 edition (changing to 2009 shortly) and requires a chimney, when repaired, to be brought up to todays codes.
Understanding that a repair needs to be completed is half the battle as a homeowner or GC. Having faith that your chimney contractors understands the codes, well, its a completely different story.
Beware, be careful and be safe.