Change In Condition type

Hi Guru,

we are creating sale order usng Tcode: VA01 with incoterm as TOP and also assign suppose condition type ZCOM( commision Agent) and then save the SO. when i'm changing the incoterm say for ex. TOP to FOr or any other type my condition type is also changing.

So I requirement is to restrict the condition type with changing the Incoterm .

Pls suggest..

Thanks in Advance...