OB52 - Authorization for specific population

Hello,

Here is the context:

At this moment in our client there are 2 group of populations: normal population and specific population (which has to be able to post some days during the month M).

We are managing posting periods through OB52 where normal population is managed through the interval 2 of OB52 and the specific population is managed through the interval 1 and has assigned  authorization group (AG1).

Also we have created different variants assigned to different company codes as each company code has different users as specific population.

The issue is that we need a 3rd group of population (for migration purposes only) to be able to post when the two other periods are already closed.

Do you have any idea how to deal with a 3rd group of population in OB52?

Thank you

Cristina