Retroactively Changing Comp Definition from 415 to W-2

Plan has never ever had an employer contribution.  Only 401(k).

Changing pay definition would only affect test results.

Revisiting 2024 (2 plan years ago).

Reason for thinking about it - Changing Definition of Comp might benefit the 2025 ADP Test based on Prior Year ADP.

A plan can allow the use of any definition of compensation defined under 1.414(s)-1 Definition of Compensation to perform the ADP test.  Assuming that the plan document does not restrict the definition of compensation, you can use any of the available definitions in this section regardless of the definition of compensation used to calculate elective deferrals or for other plan purposes.