order of rows in update

Hi,
is there an (implicit) way to make a multirow update execute on some rows prior to other rows?
It is needed in a case where a trigger is defined on the table as FOR EACH ROW, and it is mandatory
that the trigger is run for some certain rows before it is run on the rest of the rows.

Is there anything reliable to achieve this without making poor assumptions of the future
versions, or should i just "SELECT ... ORDER BY ..." and then perform individual UPDATEs?

Thanx

-- 
Achilleas Mantzios