how to update table t001b with custom program in sap abap

Hi ,

i wan to update table t001b for automatic opening /closing posting periods. i have to develop a custom program for client requirements and update table t001b directly or using standard programs RFPERIOD_OPEN OR RFPERIOD_CLOSE PROGRAMS.

here my question is ...is there any functions module to update table t001b? or any othre procedure to update table too1b..please suggest me....