The guidance you're looking for is likely in Rev Proc 2023-37. That's the current guidance covering the pre-approved program and specifically addresses good-faith interim amendments.
§6.04 -
04 Interim Amendment requirement. To promote compliance during a Cycle with a change in Qualification Requirements or Section 403(b) Requirements that affects provisions of a written plan document, a Provider (or Adopting Employer, if applicable) of a Pre-approved Plan must adopt an Interim Amendment with respect to the change within the time period set forth in section 7, unless the Provider (or Adopting Employer, if applicable) reasonably and in good faith determines that no amendment is required. The IRS will make the final determination in all cases as to whether the determination that no Interim Amendment was required is reasonable and in good faith. If an Interim Amendment is not adopted by the end of the time period set forth in section 7, the Provider (or Adopting Employer, if applicable) must correct this failure to timely adopt the Interim Amendment within two years after the end of the time period set forth in section 7; otherwise the Adopting Employer’s plan will be treated as an individually designed plan at the end of that two-year period. See section 13.05 for a Pre-approved Plan treated as individually designed.
