Basically, anything that is a combat mode or modulal action cannot be changed as I understand. This includes power attack, expertise, dirty fighting, rapid shot, etc.
This is actually false, it CAN be done, but it takes a fair bit of effort on the part of the Devs, what COULD be offered instead is what Arelith does.
Kensai
Warlocks
Path of the Sniper
Harper Scout
True Flame
Shadow Mage
Different classes based on base classes with specific benefits and consequences. Using the Shadow Mage as an example of this..a class could be made to duplicate this using the Dark Powers...Again this is the Shadow Mage as made on Arelith with the custom pros and cons:
Shadow (Weave) Mage is a path for Wizard and Sorcerer characters. It can be obtained after creating your character via selection on the path menu in the starter area, or by talking to a special NPC IG, which is strictly IG information.
Restrictions
A Shadow Mage uses the Shadow Weave to power their spells. This means:
They cannot cast any Evocation spell and Evocation epic spells. However, they can cast Darkness.
They cannot become Wild Mages (or take any other wizard/sorcerer subclass), and are not affected by Wild Magic zones.
They cannot cast arcane spells if their deity is not Shar.
Bonuses
May take levels in Shadowdancer without meeting the usual skill and feat requirements. Instead of gaining Sneak Attack from their shadow, Shadow Mages get +1 caster level per Shadowdancer level.
Shadow Mages get +2 DC on all Illusion, Enchantment and Necromancy spells.
At Wizard/Sorcerer level 20, they are granted the Hide in Plain Sight feat.