Business workflow

Hi,

I already write on this forum about my problem with mm02 and the determination of profit center with badi or user exit.

I need a solution that allow to write the profit center value within the mm02 transaction.

I tried with BADI_MATERIAL_REF but this not allow you to WRITE in the field.

Someone recommend me to use workflow task,but i don't know how to implement it.

Could you help me pls ?

Thankx!!!!