Different slopes do not break up the roof. So in the example, if the area of the repairs do not exceed 25% of the roof area, the entire roof does not have to be replaced.
The Code:
706.1.1
Not more than 25 percent of the total roof area or roof section of any existing building or structure shall be repaired, replaced or recovered in any 12-month period unless the entire existing roofing system or roof section is replaced to conform to requirements of this code.
Definition of Roof Section from FBC Existing section 202
ROOF SECTION. A separating or division of a roof area by existing expansion joints, parapet walls, flashing (excluding valley), difference of elevation (excluding hips and ridges), roof type or legal description; not including the roof area required for a proper tie-off with an existing system.
So a roof may be one section, or more. If 25% of any section needs repaired, the entire section has to be replaced. Not the entire roof, on a multi section roof.
