I once knew the answer to this a friend told me but now I forgot. If a Ninja tries to use a combat maneuver (while using Redirect Force Ninja trick) from 10ft away with a kusarigama against an enemy with only 5ft reach, could the Ninja choose to provoke an AOO when using this dirty trick? Or would the enemy have to have ten ft reach in order to provoke the AOO?
Sorry I hope that made sense.
Whether the ninja provokes is not up to the ninja and does not depend on what range he's operating at. If he's trying a dirty trick and doesn't have Improved Dirty Trick or equivalent, he provokes an attack of opportunity from his target. But if the target doesn't threaten him (e.g. due to insufficient reach) they can't make the provoked attack.
That is, it's not a question of whether the ninja left an opening, only of whether the enemy is in a position to take it.
Fuzzy Wuzzy, redirect force (Ex) actually does give a ninja the ability to decide to provoke an attack of opportunity under certain circumstances. You're otherwise spot-on.
Atalius, assuming you have Improved Dirty Trick (or something similar) and the GM permits you to use the kusarigama for said trick at said range*, the ninja can choose to provoke, but if the enemy doesn't threaten the ninja then it doesn't really matter as (a) the enemy can't take advantage of the provocation and (b) the entire point of redirect force is to take damage and use it as a bonus.
*Dirty trick normally doesn't use a weapon. That said, dirty trick is more imagination-driven than most maneuvers, and thus weapon-based dirty tricks are allowed at GM discretion. There may also be specific abilities that allow you to use a weapon with a dirty trick.