1999 Maxima,OBD-2 CODE, P0430,CAT EFFICIENCY BELOW THRESHOLD

1999 maxima shows p0430 code is there anything I should or could do
before replacing the catylitic converter? Is there a Nissan tech here
who could tell me if this solved the problem the nissan tech cited the
cause of the code to be a "program" so they wrote"mil
reprogram ECM, and coded it 555 wn it might be a pricing code. but if
any nissan  tech who can tell me what "mil reprogram ECM"
does? The reason i ask is the service engine soon light came back on
4 months later, and hey reset the ecm again and Im getting close to
the emmision warranty running out . Thanks in advance.