By-passing Number Range

Hi,

My query goes like this, I have Classic SRM Scenario Implemented, currently only 1 number range (Starting with 561..) is called when PO is created in SRM.

But now I want to call different number range(71..., 72..., ... , 79...) based on PO Created for different department.

My question is that, where to write custom code in-order to by-pass number range and calling the FM 'NUMBER_GET_NEXT' to get the number number range.

Also i have external number range defined in ECC for the same.

Screen Shots attached for reference.

Number Range path for ECC:

SPRO->Material Management->Purchasing->RFQ/Quotation->Define Number Ranges

Image may be NSFW.
Clik here to view.