So I have been planning a character for a long time that is a changeling rouge that is a infiltrator sort of assassin but I didn't want to use the assassin subclass (cause I generally don't like it) and the two that matched what I was wanting from the character was the mastermind mainly for there ability to very easily and quickly mimic others and basically go full shape shiftier or the soul knife because of the ability to manifest knives so they can't be confiscated and I really like most of the soul knives ability's while the mimicry thing is the only thing the mastermind has going for it which is why I'm leaning more towards soul knife.

But I was wondering what others thought about it.

Edit - please do not recommend other classes! Like how the person below did I really want to play a rouge and just wanted some advice on witch subclass would be best for my idea and how to build around it.

You might consider playing a College of Whispers Bard. Not only do they get a sub-class ability allowing them to mimic others, but Bards are a Charisma-based Expertise class (all of the relevant skills for what you want to do are Charisma skills).

nice recommendation but I've always thought of whisper bards as spreaders of misinformation and gathers of dirty secrets rather than strait up assassins so more of instigators than killers.

for example I imagine a whisper bard to inspire false fear in the masses like a walking propaganda poster, or get close to a noble so they can get black mail about that person to use later.

While I wan't my character to do some of that but instead end with the target dying instead.