I have shifted I Will Not Yield to level 2.
Barring, of course, the alignment restriction. I have added in Concentration ranks (8) as a pre-req in addition to Diehard (even though it basically becomes obselete when the Immortal hits level 7 and the secondary effect of I Will Not Yield kicks in.
And here is where the same argument that I had with Lix comes in. Because, yes, file off the fluff and this becomes generic. But here's the thing. If you file off the fluff, you destroy the class as it has been written to be. It is really that simple.
Prestige classes exist to be more complex to enter, to be something that it takes a degree of directional character building to reach. This is deliberate, and is one of the few things that makes them special compared to base classes. What you are saying above, regardless of how you have framed it, spits directly in the face of that ideal.
Why do you think that 3.0 and 3.5 Faerun PrCs are sometimes hellishly restrictive in their ability to enter? And why, perhance, do you think people still take those incredibly restrictive classes? It's because that, at its core, the PrC system is designed to reward focus. It's designed to reward the playing of a character just as much as it rewards the building of the character on paper - quite possibly more so to the former. And this, here, is the thing that I'm trying to say.
If a DM takes this class and decides to "waive alignment requirements as the silliness they are." then the class isn't an Immortal anymore. It's just a generic, incredibly-hard-to-kill beatstick. Sure, you can give it alternate fluff. But that does nothing to the statement that I have already made in that it is, at that point, no longer an Immortal in any sense of the term.
An Immortal is not what they are because they are, themselves, powerful. They do not become what they are through a need for self-empowerment for the sake of self-empowerment. An Immortal, by their very nature, becomes powerful so that they can protect. A person, an ideal, a nation, a miniature giant space hamster, whatever. They become stronger through channeling their Light through that utter commitment to that ideal. And that sort of commitment is, by definition, Lawful.
A lot of people look at Lawful and assume that they have to follow the rules of the land, or a lord, or an outside force or code. Lawful is none of those things. Lawful is the following of a creed, the commitment freely granted to a shield-sib or even one's own family. Those are all Lawful concepts. Because when it comes right down to it, the primary example that most give as a Chaotic Good character (well, that I've heard at least) - that being Robin Hood - is far more Lawful than Chaotic.
And that is the same way that Immortals are always Lawful over Chaotic. If you want a nigh invincible warrior of Chaos, play a barbarian. Or make a ToR PrC that lets you do that, because the warriors of Chaos are innately aggressors. They aim to destroy those attacking themselves and those that they might protect. A Lawful character - at least in the matter of an Immortal - exists to protect those under their care, or the ideal that they've devoted themselves to or etc. etc. etc. You get the idea.
Now here's the most important part. Can an Immortal be an aggressor? Yes, they can. But Immortals, in contrast to the idea of Barbarians, attack through defence. Barbarians in this system are charging death machines. Yes, they're very hard to kill, but the primary purpose of a barbarian in regards to what their class is able to do, is to kill the enemy. That of an Immortal...is very different.
So I thank you kindly for your opinion, but I disagree absolutely and totally with it.
Which is a big part of why the alignment restriction existed. Also part of why I've taken some of your advice in regards to pre-reqs. But there's a bigger point here - and it's one that really needs to be addressed.
You're making these assumptions from a character creation point of view. Now yes, that's fine and all. But when it comes right down to it, that's not what PrCs exist for. Hell, that's not what multi-classing exists for. Both of these things, interlinked as they might be, exist for the growth of the character that you have brought into being. And those choices are meant to fit the character over the player.
The class and level of a character are part of them and - yes - do in some way define them. But there is so much more to it. And I know you know that Selinia.
Regardless. I have fixed it as much as I feel ok with.