I assume you are asking if you can customize your Elite armor in Halo 3 multiplayer to include the katana? No you cannot.
http://hubpages.com/hub/Halo-3-Armor
No, there is no armor in Halo 3 that has a knife in the shoulder.
There is no Brute armor in Halo 3, only Elite and Spartan models.
go to http://hubpages.com/hub/Halo-3-Armor
All of the regular armor can be unlocked by beating the campaign on legendary and collecting all skulls. You can get the Katana (sword) on your back be getting the origanal 1000 gamerscore. There's also recon armor, which can only be unlocked if Bungie (the makers of Halo) give it to you.
you get all the vidmaster achievements on halo 3 and halo 3 odst
To get the Katana as an armor permutation in Halo 3, you need to get 1000gp in the game. The new achievements released for Halo don't affect it. The easyst way to get it is to get all the "old" achivements.
NO
recon armor
the same way in halo 3 because when you play halo 3 mythic it says your playing halo 3
there is no permanent cheats in halo 3. you need to unlock them by achievments. and, you can not get the flaming armor effect, it is only for bungie employees. in halo reach, buy the legendary package to get that armor effect.