Account Assignment category K(Cost center)

Create a validation rule that will check for the proper conditions.

SPRO -> Controlling -> General Controlling -> Account Assignment Logic -> Define Validation

Create your rule here, and any other appropriate steps to follow as part of the validation. Your prerequisite could look something like this:

SYST-TCIDE = 'ME51N' OR SYST-TCODE = 'ME52N'

This to ensure the check is occuring at time of PR create or change via ME51N or ME52N.

The check logic could look like this:

COBL-AUFNR >= 'whatever number range'

This to ensure that the order will be whatever range you have set for the desired statistical order, or however you identify these. You can get pretty creative in these two areas. Following this, you will want to define the message type that results from the above statements being true (cancel, error, warning, information) and whatever message text you want to pass.

Good luck!