Auto Pricing procedure changes in VF01

Hi to all,

Now i am working on billing VF01, here the requirment is when the creation of new billing, (based on price) need to change the pricing procedure automatically.

I have a logic to check the condition, but i am not finding the way to change the pricing procedure.

Example.. if Pricing procedure is 'A', If condition satisfied need to change the pricing procedure to 'B'.

Thanks in Advance.

With Regards

Anand