30 CFR § 33.12
Changes after certification.
If an applicant desires to change any feature of a certified unit or system, he shall first obtain MSHA's approval of the change, pursuant to the following procedure:
(a)(1) Application shall be made as for an original certificate, requesting that the existing certification be extended to cover the proposed changes, and shall be accompanied by drawings, specifications, and related data showing the changes in detail.
(2) Where the applicant for approval has used an independent laboratory under part 6 of this chapter to perform, in whole or in part, the necessary testing and evaluation for approval of changes to an approved product under this part, the applicant must provide to MSHA as part of the approval application:
(i) Written evidence of the laboratory's independence and current recognition by a laboratory accrediting organization;
(ii) Complete technical explanation of how the product complies with each requirement in the applicable MSHA product approval requirements;
(iii) Identification of components or features of the product that are critical to the safety of the product; and
(iv) All documentation, including drawings and specifications, as submitted to the independent laboratory by the applicant and as required by this part.