Can I reopen the closed period for comparing the results of cost accouting chnage at Test Server?

My customer would like to change the cost accouting Splitting method by the Business environment change. We can compare the results of the cost accounting chaned at TEST server for just one month. we would like to compare the results at least sequential 6 months.
Please let me know how can I test the results of cost accounting system splitting method changed with sequentail 6 month with past or future data at Test Server.

Can I reopen the closed 6 month before period and re-calculated the cost accouting system? Or is there anyway to incremental backup?

Kind Regards,

JungSook Lee