Automatic enrollment and grandfathered plan

If a pre-enactment (grandfathered) plan without automatic enrollment now chooses to add automatic enrollment, does it have to be an EACA and comply with the SECURE 2.0 rules?  Or can the plan add a plain vanilla ACA without any problem?

Thanks.

The pre-enactment plan had a 401(k) feature and is grandfathered.  SECURE 2.0 did not say that any modification to a grandfathered plan had to be an EACA.