When I read the stat block on Master Lodaka's Lightsaber a thought popped into my head, What if I let my players if they are dedicated to the modification of their Lightsaber that they could get a ultimate item quality like ignore cotorsis. What I'm wondering is how to make this balanced and what other Ultimate qualities we could come up with?

I think you'd run into problems keeping it balanced. The items in NoP are artefact-level "magic items" if you will, and allowing players to craft gear with qualities like those could very quickly get out of hand. Just my personal opinion, mind.

Something like Ignore Cortosis seems a bit Darkside...

In any case I agree with Krieger22, you'd really start wobbling on the edge of Munchkin gorge if you start down that path.

Oh I was fully intending it to be a late game thing, I would make whichever player that wants a Ultimate quality on their saber jump through several hoops. I was using Master Lodaka's saber as an example, I never intended for all these qualities to be so powerful.But I do see your points that it could be unbalanced.

Things like that take a lot of playtesting to get right. There are a lot of data points you want to consider... enough that you really need several people trying to break it within the context of the rules to see if it will survive contact with your players. Powerful PCs in possession of really powerful equipment can have dire effects on a game; it takes a very focused, mature group to keep it from devolving into an entirely different sort of game. If you're familiar with the phrase "jumping the shark," then allowing really high-powered items is usually that moment for a campaign (in my experience - your mileage may vary).

The main reason for this is because my party is wanting to eventually challenge both Vader and Palpatine, so I want them to have at least a sporting chance. However I think I'll just wait till they get much closer to that to consider any like this, we've only had like 3 sessions but I'm just trying to imagine how they can even attempt to challenge them. I was also under the impression that I could just make some enchantments like I do in D&D, but alas you guys have convinced me to reconsider.

The main reason for this is because my party is wanting to eventually challenge both Vader and Palpatine, so I want them to have at least a sporting chance. However I think I'll just wait till they get much closer to that to consider any like this, we've only had like 3 sessions but I'm just trying to imagine how they can even attempt to challenge them. I was also under the impression that I could just make some enchantments like I do in D&D, but alas you guys have convinced me to reconsider.

So, a couple things. A fully upgraded lightsaber is pretty vicious, and your players will have some powerful characters by the time they get them. Second, statting out Vader and Palpatine is up to you. Just be sure to take their measure against a few inquisitors to see what they can handle, and then push it past that.