Routine for restricting the Duplicate condition type in PO

In PO, we have condition tab there are various condition types. requirement is that - a particular condition Type should not able to use/entered manually multiple number of times in PO-Condition. I like to know the routines or user exit where I can control this.

For Ex- FRC1 is there PO then nobody should able to add one more FRC1 condition type manually in PO.

There was suggestion on previous discussion but very less insight on Routines which can be used or how can be find out it?

This was old thread -

"Check routine or design to write a routine & assign to Freight Condition - ZFR1 in M/08( in MM Schema), so it should not enter again or not possible to enter by user(can appear only once)."

Please suggest me the routine for this or where I can find out this?