The field aggroradius in the npctypes table is what you need to change. You can do it one at a time or all at once.
Here is an example.
Code:
update npc_types set aggroradius = 50 where name = 'an_elven_skeleton' and id >= 54000 and id <= 54999 or name = 'orc_pawn' and id >= 54000 and id <= 54999;
That changed the aggroradius of the orc pawns and elven skeletons in Greater Fardark only.