if you want add it in halo custom edition you create a map
or you can add just the elite in halo combat evolved
for halo custom edition use the Halo editing kit
for halo combat evolved use halo map tools or other programs
at this link there's a tutorial how to import the texture in halo combat evolved:
http://www.xgclan.com/forum/index.php/topic,356.0.htmlthe process is similar
for halo custom edition ask to altis-sensei xD
he create maps and i think he know how to do that