Availability based on minimum shelf life

In 'VL01N ' t code batches are selected based on the parameter value 'LOBM_RLZ(min. shelf life)'.

I have an requirement in which this minimum shelf life is also maintained in LIPS table (LIPS-ZZVSD_MVZ).

If this field is maintained with some value which is different to tha parameter value LOBM_RLZ, then batches

should be selected according to this value. Else needs to be selected as per LOBM_RLZ.

Kindly help me to find out the exit to write the code and how can I overwrite parameter value LOBM_RLZ?