FM MPLAN_CHANGE to change matenance plan

Hi,

I'm trying to use the Function module MPLAN_CHANGE to update the value of the field STADT (Start Of Cycle) for a particular WARPL(maintenance plan). But its not updating the database table (MPLA), but instead, its storing the value in some temporary buffer area. What could be the reason for this?

Is there any other function module or BAPI to update STADT for a particular WARPL?

Thanks in advance

Sreeraj