"""Reaction field changing from error to warning is also not acceptable as it will work for all cases irrespective of customer has balance or not. User can play with it. My Business is not allowing this""""
You can make customer specific credit checks too by using Customer credit groups(in addition to Document credit groups) in FD32 in status view.
If at all you want completely the credit check has to be skipped--then assign your logic in requirement field in OVA8.
Hope this helps.
Phanikumar