Here is a link to several posts from a few years ago discussing splitting a plan to avoid an audit: Splitting Plans to avoid audit
It includes comments from those who have done this. Note that all of the comments focus on how to split the plan prospectively including steps to take to mitigate possible challenges to the process. There are several comments about the DOL and IRS perspective on how to count participants as of the beginning of the year. Basically, they will look at facts on the first day of the plan year and a plan cannot alter those facts.
My take is the plan will not succeed in trying to alter, with a retroactive amendment, the participant counts as they stood on 1/1/2022.
It will be interesting to see if anyone has had any more recent experience on the topic.