Says in my 3.5 MM that Spell Immunity is exactly like spell resistance, except that one can’t overcome it. Thus it can presumably be lowered, exactly like spell resistance.
It would be bloody silly to have it unable to be lowered, because then you couldn’t repair your golems.
I only tell you what I think I remember. I will, if I remember, check, the current D&D Rules FAQ and Errata on the subject.
Sorry, on a reread I see that that post came over a little harsh. Didn’t mean to snap at you. I’m just getting a trifle irritated at how collosally broken D&D magic is, and how a lot of the attempted fixes just make it worse.
<chants to self> My magic system will work. It will be sane and not be broken. I will think through the consequences of my rule, and remember that playtest is my friend. My magic system will work…</chants to self>
It’s almost impossible to use the 3rd edition D&D spell Shapechange without munchkinning. The spell gives you all of the extraordinary, but none of the supernatural, abilities of the creature you turn into. And the size limits on the spell are so large as to be laughable: I don’t think there’s anything in the Monstrous Manual too big for it.
Now, consider the infamous Tarrasque. In 3E, almost all of its abilities are extraordinary, presumably to stop players from depowering it with Anti-Magic Shell or the like. But this also means that all of those ungodly abilities are available via Shapechange.
But, of course, no munchkin in his right mind would ever dream of shapechanging into a Tarrasque. Why not? Because a true munchkin would use a template. Like, say, half-dragon, which can be applied to pretty much any living creature. If you change into a half-Tarrasque, half White Dragon, then you get all of the Tarrasque’s standard advantages, a few extra points to your physical stats, clumsy flight, and a mediocre breath weapon. Oh, yeah, and also immunity to cold, which is darned near the Tarrasque’s only vulnerability. You could alternately do Black Dragon, for acid immunity, or the metallic equivalents (unfortunately, although Silver Dragons are immune to both acid and cold, half Silver Dragons are only immune to cold).
Pah! Templates are for amateurs! In my experience, most true munchkins are going to take a page from Knowed Out, above, and shapechange into a ten-bajillion-ton ball of adamantium and fall onto their enemies.
That, and the polymorph spells, pretty much require a steady DM at the wheel.
Daniel
The 3.5 Shapechange is even worse. It puts an HD limit on it, which is good. However, you do get the spell-like and supernatural abilities of your target form. It’s absolutely obscene.
We’ve tentatively settled on a 3.25 version. Extraordinary abilities only, but the HD limit from 3.5. It’s still pretty powerful, but this eliminates the worst of the abuses. Not that it’s going to come up any time soon - we haven’t got any ongoing campaigns with anyone able to cast 9th level spells.
In the SRD, it mentions that golems have "magic immunity:
This is unlike spell resistance, inasmuch as it applies to supernatural effects as well, and doesn’t mention any ability to suppress the immunity. Fire-immune creatures can’t choose to become susceptible to fire; I don’t see any indication that magic-immune creatures could choose to become susceptible to magic.
It does mean that reparation spells would need to be listed as something the golem is specifically susceptible to.
Daniel
I think that’s the 3.0 SRD, unless something’s changed - I recall distinctly that in 3.5, I was dismayed that the golem immunity had been specifically changed to exclude supernatural abilities - something I thought silly, since they were now susceptible to Dragon’s breath, for instance.
I’d like to note that a couple of the golems already have spells listed that restore hitpoints - also, unless I’m misremembering something, as creatures, they will heal naturally over time.
What’s the most absurd character you can generate using D&D 3rd-edition rules?
From the above link, thanx to Journeyman for THIS LINK to the following:
Well, I looked it up, as I should have before replying… the 3.5 SRD indeed includes supernatural effects… which means, if memory serves, it differs from the 3.5 Monster Manual in that regard. Will have to look when I get hom in half an hour or so.
Strangely, the description of magic immunity in the text of each golem doesn’t mention supernatural effects and makes it sound much more like unbeatable spell resistance. What I quoted, the listing under generic golem traits, is very different. Is this a typo in the SRD?
I prefer the idea of golems that cannot choose to lower magic immunity: letting them do so makes them seem too sentient for my tastes.
Daniel
Ah, here’s the problem. The generic text for Golem in the MM3.5 is the same as the SRD - mentions Supernatural effects. The specific text for each golem omits the supernatural part.
And it isn’t spell resistance. It’s spell immunity. Spell resistance can be lowered… spell immunity cannot be (for nowhere does it say that is allowable). - So I think the golem trick won’t work. At least, not with ME as GM. 
To pick nits, it’s actually magic immunity: spell immunity is a cleric spell that specifically functions like unbeatable spell resistance. The SRD doesn’t define magic immunity anywhere besides the golem description, AFAICT.
If anyone else is still reading this, yes, we D&D folks really are this dorky. I have these kinds of discussions every day in the D&D rules forum. 
Daniel
It wasn’t really that bad. It was a playtest-type game where we were allowed to come up with anything simply to test out various systems we’d created. We found a few loopholes, which will be closed in the final version. Really, people weren’t supposed to use them all that once! ^-^
And mostly whatever powergaming we did was pointless, since the GM was much, much better at it than any of us. He never used off-the-shelf monsters and had plenty of opposition for us. Our numbers and adventures were rather overpowering, but in practical terms the game wasn’t that much different from any other. The best solutions always relied on cunning, planning, and adaptability, regardless of how powerful the character’s spells were.
I was about to express my amusement at how the discussion of “powergaming” had morphed into a discussion of “munchkinism,” until I went back and reread the OP:
Yep… that’s the primary MO of a munchkin.
If you ask “what’s a munchkin,” then you probably are one… at least according to this.
Just so you know: 3.5th Edition has done away with Damage Reduction of the 15/+1, 10/+2, etc. variety. Instead, you’ll now see Damage Reduction such as 10/magic, which can be overcome by any weapon of +1 or greater enchantment.
However, they’ve also added Damage Reduction of the form “10/epic”, which requires at least a +6 magic weapon to overcome.
Believe me, I know. I have every WotC D&D 3.5 book released to date.
For those of you who are confused by the “Spawn of Fashan” references in the above link, I did a playtest review of The Spawn of Fashan a couple of years ago.
<nitpick>
adamantine = super-tough metal in D&D 3rd Edition
adamantite = super-tough metal in AD&D 1st & 2nd Edition
adamantium = super-tough metal in Marvel Comics
adamant = super-tough substance mentioned once or twice by Tolkien
</nitpick>