I believe the answer is that it is allowed by the following:
13.1 AUTHORIZED MODIFICATIONS
If a modification is not specifically authorized in this or previous Sections of these Rules, it is not allowed.
The addition of small holes for attachment hardware for authorized modifications is implicit (e.g., holes for fasteners to mount additional gauges, holes for brackets to mount shock absorber remote reservoirs, etc.). However, these holes may serve no other purpose.
All repairs must comply with factory-authorized methods and procedures, or industry standard methods, as follows: If the OEM does not provide an appropriate method of repair, industry standard methods and procedures may be used. Such repairs may not result in a part or combination of parts that provides a competitive advantage (e.g., significant change to weight, suspension control, power, etc.) as compared to the standard part(s). Competitors are strongly cautioned to use this allowance to make common-sense repairs only.