If the amendment is specifically authorized by the prototype (or, in some cases, volume submitter) document, such as the in following (from the Corbel VS prototype-style Basic Plan Document):
"The Employer (and every Participating Employer) expressly delegates authority to the sponsoring organization of this Volume Submitter Plan, the right to amend the Plan by submitting a copy of the amendment to each Employer (and Participating Employer) who has adopted this Volume Submitter Plan, after first having received a ruling or favorable determination from the Internal Revenue Service that the Volume Submitter Plan as amended qualifies under Code Section 401(a) (unless a ruling or determination is not required by the IRS). For purposes of this Section, the mass submitter shall be recognized as the agent of the sponsor. If the sponsor does not adopt any amendment made by the mass submitter, it will no longer be identical to, or a minor modifier of, the mass submitter plan."