cant find the tut i used to do it
but went something like this
Make a profile on halo with close to the right amount of letters you want for you new name(easier this way)
Transfer the save over to you pc and open the blam file and savemeta file in a hex editor
now open MS word and insert>symbol the box with symbols will show up in the bottom right change the from box to ASCII(hex) you will see the box that says "character code" the 2 letters there are the hex code for that symbol
Change the name in both the savemeta and blam files to exactly the same thing and save both
Now you need to resign the save to make it work
Resigner hereafter you downloaded the resigner open the resign.ini file and add this entry in there
Halo:
[4d530004]
ID=4d530004
Title=Halo
AuthKey=5770E155A1C75FA9830B141896544428579AF1E6
DataFile=blam.sav
SigOffset=48
DataOffset=0
DataLen=48
found by brenj over at xbox-saves.com
Open up the resigner and and choose halo from the drop down menu and browse computer for the blam file to resign
that should be it and it should work
trying to remeber it off the top of my head so if it doesnt work let me know
edit: link fixed