solution for one scenario

Hi Gurus

I want a solution for this scenario.We have a product which can be produced in the production line A and production line B also.I have a requirement qty 1000 to produce.Today i want to produce 800 qty in production line A and next day i want to produce 200 in production line B.How to configure the routing or hw to configure the scenario.Plz suggest me.

With regards

Dambarudhar