Third party PR creation routine

Hi SD experts,

My requirement is when ever a third party sale order is created PR should not be created ( Mean it should be on hold).

Once the delivery block is removed PR should be created. ( I will define define delivery block it header or item level)

I found a solution that modify the 102 routine in OVB6 transaction.

But i cannot see a copy or new entry option in OVB6. ( New entry field is Grey mode).

My question is how to copy this 102 routine and assume if i create 902 copy of 102 where to assign this 902.

I dont know where is this 102 routine assigned in SD configuration.

Request all of your feedback.

Vimal