Quantity Split to two vendors in one PR

Dear Experts,

I have a query, during MRP Run following is the scenario.

PR Generated for AA material for 1000 nos for xx vendor.

Now we want to split quantity 600 to xx vendor and 400 to yy vendor. We have not maintained the quota, as we rarely procure material from yy.

Do we have to change the quantity in PR manually and add one more line for yy vendor. OR can we control it while doing ME57 OR ME59N.

Thanks in advance.

Ishu