How to unenroll people from the absence plan

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Hi all,

            We have a couple of locations for which we are moving people in those locations to a different absence plan and hence starting 1/1/2020 we would like to unenroll them as of 12/31/2019 last date. Can anyone suggest what will be the best method to achieve this unenrollment. 
My idea is

1.Update the eligibility profile to exclude that site

2. Run the enrollment process as of 12/31/2019 .

 I am confused about whether the enrollment process should be run as of 01/01/2020 or 12/31/2019.

Is there any other alternative to this.