Xenon.7 (DeToX) released tools to remove security checks from your Halo 3 & Halo 3 ODST executables, so u can modify maps and make your own. Of course don't use this on LIVE, MS can and will detect it ... anyway, you shouldn't go on LIVE with a homebrew360 (freeBOOT/XBReboot) at all as MS can easily detect that too:

This bundle of hacked halo 3 executables will allow you to run your modified .map files in Halo 3 and Halo 3 ODST, which was not possible prior to XBReboot because Bungie had implemented RSA checks. This executable removes those checks.

NOTICE!!: These executables have already been patched with updates.. so this package will contain Halo 3 1.0, 1.1, 1.2, and Halo 3 ODST. So if you have an update for Halo 3/ODST, you might want to clear your cache (Tutorial here), so that the update does not try reapplying ontop of the already patched executable, or it does not interfere with Halo 3 1.0, and etc.

This tool will auto detect if the XEX you opened is not a clean one, and will not proceed if it isn't.

Items & Descriptions
* Halo 3 1.0 Hacked - Ability to mod .map file.
* Halo 3 1.1 Hacked - Ability to mod .map file.
* Halo 3 1.2 Hacked - Ability to mod .map file.
* Halo 3 1.2 Ultimate - Ability to mod .map files, All armor is always unlocked(properly), alot more security removed from .map files, which, at times, would give you a dirty disc error, because the engine is really picky. Removed signatures on .blf images(mainmenu preview images), .mapinfo files(files that add .maps to your mainmenu). Alot more aswell.
* Halo 3 ODST Hacked - Ability to mod .map files. I believe I also removed a bit more security here than that that made the engine less strict about certain header values that are to be calculated.

HOW TO APPLY PATCHES TO THE EXECUTABLE
-Put xorloser's xextool.exe in the same folder as this application or else it will not function.
-Open H3Unlock.exe, open up a clean XEX from Halo 3 ODST or Halo 3, and select which patch you'd like to apply.
-Click apply
It's also been reported you should use xextool for all 4 .dll's:
-\WaveShell-Xbox.dll
-\WavesLibDLL.dll
-\waves\L360.dll
-\waves\Q10.dll
Official Site: n/a, by Xenon.7 (DeToX) & Anthony on forums.xbox-scene.com