Once the values are transferred to demand management either manually or from SOP to Demand Managment,i.e to MD61,then you can rearrange the values to your convenience.
For Eg: In MD61 you have given demand values for an FG material from October to January 2008 on monthly basis say 100,100,100,100.
Using planning table MF50 - Change mode,you can change these monthly values accordingly to your wish say 80,120,70 &130 and if u run MRP you will be getting planned orders RE type as per the values given in Planning table,If not maintained in planning table then as per the values in MD61,planned orders get's generated.
You can change few of the Monthly demand values into weekly,daily,shift or as per to the Planning calendar.
For this you have to choose the options in MF50.under period & Calendar.
Some T codes Related to Planning table
MF50 - Change Mode
MF52 - Display Mode
MF57 - By MRP Lists.
MF51 - Production List