scripting a factions strategy?

Does anyone know how to use the script files to influence how a faction, such as Sassanids, expands on the campaign map?

In my games of BI they always expand massively to the North and East then attack europe through Germany/Balkans, I was wondering if it would be possible to use the script files to put a 'virtual wall' (:wall:) to their North and East to minimize their expansion in these directions and encourage them to attack directly west?

I know that:


faction parthia, fortified henry
denari 45000

(R:TW script)

The fortified Henry (IIRC, and to my best knowledge) does not affect how they expand, but what they build and/or their army composition.