Have you tried overriding the getEjbql() method?
Yes, I think getEjbql() is invoked at the end after evaluating the value expressions,
I wonder if it's safe enough to modify the restrictions via 'setRestrictionExpressionStrings' in getEjbql() as well.
Please suggest how you managed it. I need to customize "Search" functionality from xxxxList.xhtml page (default generated by seam)