[cavedude]

SQL queries would do it. In your example, at a MySQL prompt do:

update npc_types set hp = hp - hp*.3;

If you only wanted to do this for mobs higher than say level 19, you'd do:

update npc_types set hp = hp - hp*.3 where level > 19;

For all undead mobs higher than level 19, you'd do:

update npc_types set hp = hp - hp*.3 where level > 19 and bodytype = 3;

Etc, etc.

That's the basic syntax you can use for most mass npc editing, browse around the forums for more examples and advanced functions.