I want to redo my whole Oblivion installation from scratch, but that means I need to back up my DLCs since I don't think the executable installers will work a second time around - correct me if I'm wrong, as this will definitely make the rest of the post moot.

Here's the problem. I -might- have altered the .esps with TES4Edit in a way that I can't easily revert. If I did, I deleted the backups that TES4edit made. This isn't a mistake I intend to repeat, but the fact is, if it's done it's done. If someone can post a CRC of each DLC ESP (except Horse Armor, since I never got that one) so that I can take a CRC of the ESPs I have and compare, it would be much appreciated. If I haven't made this stupid mistake, then all is well and I can just back up the .esp and .bsa files for the DLCs and all will be well.

However, if I did edit the DLC ESPs, what can I do to get the original ESPs back, or automagically revert the changes I made? Please don't suggest anything illegal, and I'm quite adept at determining which methods are legal and which aren't.

You can run the executables as many times as you like. Those were the first "backups" I had for them.

The DLC installers are known to not work on 64-bit Windows, but if you're running 32-bit it should be OK to just reinstall them.

Afterward, it'd be a good idea to back up the installed DLCs, in case of future accidental changes or if you move to a 64-bit OS. (I made a BAIN archive of them and marked the file read-only.) Don't forget to back up the .bsa files in addition to the .esp files.

Well I'm running Windows 7 64-bit now. If it comes down to it I could install the game on one of the XP machines around here and run the installers on that, then back the files up that way.

I can back up the .bsa files now, since I definitely never touched them, but I'm just not sure about the .esp files. I wish I had made an OMOD of the DLCs when I was thinking about it, long before I started messing with altering ESPs in TES4Edit.

Yeah...maybe you could boot linux from a USB drive or something, haha. I OMOD-ed the DLCs immediatly, OMOD-ed everything really... Now, everything is being BAIN-ed...that is not still collecting dust in its old OMOD shell. (The compression is nice for storage.)

Here are the checksums you asked for, in the form of MD5 hashes:

fee130f1cfd8b535928eca72dca4a0c4  DLCBattlehornCastle.espcf020d66d0c5b90e52dd03dfe7adfef4  DLCFrostcrag.esp12733ad9718557860ae8c14bc7eb11ca  DLCHorseArmor.esp5ed2beaa1c6930fa8e7acd3e28d3965d  DLCMehrunesRazor.espd4e363c4cbf3b39320ed0590322a72a2  DLCOrrery.esp6bad4b26b199d62ab2f9f38c3552893b  DLCSpellTomes.espa938166d6318e2606dc4cbdb9ccc6960  DLCThievesDen.esp2c51ff6c5196a334377f41a5ec7159e5  DLCVileLair.esp4187dc56a5620815f4ea6bf8576dbf4e  Knights.esp

You can use http://www.pc-tools.net/win32/md5sums/ to verify them.

I fail to see why your possibly having edited the ESPs is an issue if all you're going to do is backup your Data folder for a game reinstallation.

I want the esps back in their original state so I can do it right, with a Bashed Patch, rather than randomly editing mods to be compatible with each other.

Wyzard256, thanks for the checksums. It looks like I have, indeed, edited some of them >.<

Now if I can only figure out where I stuck those installers. They aren't in the usual location...though I have found the text file with the activation key for two of 'em

The activation key is for the download, I guess. You certainly do not need to enter a key to run the installers.

Not sure why I didn't think of this sooner. I just opened all the DLCs in TES4Edit - and none of them are dependent on anything except Oblivion.esm. Whatever I may have edited, it's not gonna be significant enough to prevent me from doing this, since all I was really worried about was nonstandard dependencies.