How to ... angry casters and Hero resistance?

These are the questions for pro map makers.
1. As you know, all heroes and creeps starting from level 7 have resistance to spells (creeps use "Hero" data from spells). I want to either remove or change the level it starts from Creeps' Spell Resistance. How? Note: In Gameplay Constants and Object Editor there's no way to do that - or at least I didn't find one.
2. Computer controlled Spellcasters don't use spells as much as they should. For example, a caster may have cripple, 100/2500 hp, 1000/1000 mana but will NEVER cast cripple on attacking hero. I want to make spellcastig units to cast all of their spells before they run out of mana and only then they should attack enemy Hero using normal attacks. Anyone knows how to do that?

Your first problem is simple... remove their 'resistant skin' ability. You'll find that all units above level 6 have it.
The second problem sounds like an AI problem. You'd need an advanced AI.