Retroactive Amendment to Exclude HCEs

Plan Administrator wishes to exclude HCEs from participating under the Plan in order to pass minimum coverage tests under 1.410(b)-2(b)(6).  In order to avoid minimum coverage failure for 2021 Plan Year, Plan Administrator proposes adopting amendment to exclude HCEs retroactively to 01-01-2021.  The Plan does have one HCE currently participating the Plan.  If the Plan Administrator adopts the amendment, can the deferrals for 2021 year be refunded to the HCE (and included in gross income of the HCE), since the HCE is no longer eligible, so that no HCE benefits under the Plan for the 2021 plan year and the Plan passes minimum coverage?

Any problems or issues with this I am missing?

You can exclude HCEs from deferring prospectively, but not retroactively. 411(d)(6) prevents cutbacks of benefits already accrued, even for HCEs.