This is for H3 on 360 right?I already helped out 2 people getting rank 50, so I figured I'll make a post here to help out others.
Post or send me your GT and I'll make your max rank 50 in Halo 3. You don't need to be online or be in a lobby. This will not give you additional EXP nor change your rank in any playlist. It's an age-old modding trick and it's a bit glitchy, so you might need to switch between lobbies to make it appear. I don't know anyone who has been banned for this and it's pretty unlikely you will be since the rank will be meaningless by December, but there is always a risk.
I don't believe posting this is against the rules, but please take this down if it is.