How to implement Custom / Scripted Conflicts in Siebel eConfigurator

We have a requirement to evaluate custom rules and not allow product changes if the custom rule fails. One example is say if qty of a product selected in the current econfig session is more than N then an error/conflict needs to be raised and suppressed automatically by returning Resolution="UndoLastRequest" in Cfg_OnConflict It is observed that any OOB conflict getting generated due to MAX cardinality at the relationship level in the product bundle are handled correctly through this way. But for other cases where custom scripted validation is implemented and a RaiseErrorText statement is executed in Cfg_ChildItemChanged / Cfg_ChildItemSelected it