how to write OLAP Variable which used in infopackage

Hi, experts,

I only know CMOD can write User exit for report variant. right now I wanna set fiscalyear/period from XXXX001 to XXXX( current period minus 2) -- XXXX is fiscal year

how can I write this rule into customize OLAP variable, then I can use it in each of infopackage.

Thanks in advance