I believe what will decide your Duster's final design is the side you talk about when you try to convince Ulysses not to go through with his plans.
The trick is to wear that faction's armor (like NCR Trooper armor or Legion Armor) and it will reset your rep with them to neutral. Thus if you've been good on the Strip, you will be talking about Vegas, not NCR or the Legion. And thus you will get Mr. House's or Yes-Man's symbol and ability instead.
I tested this out myself wearing the NCR Engineer outfit and it worked. My two last saves got me the NCR Bear symbol. But when I put on the NCR outfit (Before and after the battle), I got the symbol for Mr. House this time around.
So this tip is for anyone who wants House/Yes-Man faction duster without lowering NCR or Legion rep. --- Mass Effect 2: Will Trade Terminus Armor Code for Collector Armor Code. E-mail me at firstname.lastname@example.org
No prob. Not that the Bear's effect isn't good; I just wanted to look more fitting for supporting Mr. House. --- Mass Effect 2: Will Trade Terminus Armor Code for Collector Armor Code. E-mail me at email@example.com
Wow awesome. It sucked when I got the Legion Bull on my Yes man character. So do I only have to be wearing the faction armor during the last conversation with him? --- Currently playing: Prototype, Elder Scrolls 3: Morrowind, Tropico 3, Deus Ex: Human Revolution
Yes. You'll know it'll work when you see the Vegas speech check instead of Legion. You can take off the armor during the following battle, and then put it back on before you go to the missile computer and make your desicion about its launch (just to be safe).
It appears that the Courier Duster will be marked with whatever side speech check you are capable of using when you talk to Ulysses. --- Mass Effect 2: Will Trade Terminus Armor Code for Collector Armor Code. E-mail me at firstname.lastname@example.org
So if you've still got the save there, would you be capable of checking if wearing Legion armour will allow you to get a Legion duster without actually having high Legion rep? As an experiment primarily. --- "Anywhere is within walking distance, as long as you have the time." [The Official Robert House of the Fallout: New Vegas Boards]
For Yes-Man, I believe you'd have to kill Mr. House first so Yes-Man becomes the Indendent faction head instead. Then you have to have more Strip Fame than NCR or Legion fame. As long as both sides don't like you more than the Strip, you can simply wear the higher faction's armor to set your fame to neutral. It will count and make your Strip fame the highest.
As for getting NCR when you're working with the Legion or vice-versa, you'd have to be not hated by the other side. Essentially, this trick only works to temporaly set your unwanted higher faction fame to neutral. The side that likes you the most is what decides your specific Courier Duster.
Remeber, whatever faction you'll talk about with Ulysses in your final confrontation is the one you'll get the Duster for. Save before your talk and reload if you don't get the one you want (so you can get the proper disguise ready and adjust your faction fame if needed) --- Mass Effect 2: Will Trade Terminus Armor Code for Collector Armor Code. E-mail me at email@example.com