Mealamu was originally suspended for four weeks after being found guilty of intentionally striking Moody - a penalty that would have ruled him out of the three remaining tests, starting with Scotland at Murrayfield tomorrow (6.15 Sunday NZT).
The New Zealand Rugby Union decided to appeal the punishment imposed by IRB judicial officer Professor Lorne Crerar and after a three-hour hearing Mealamu and his legal team succeeded in having the charge downgraded from intentional to reckless.
He misses the Irish test in Dublin next weekend but is free to play the All Blacks final match against Wales in Cardiff on November 28 (NZT).
Mealamu is also eligible again to make a lucrative guest appearance for the Barbarians, who play South Africa at Twickenham on December 4 - a match covered by his original suspension.
Hika Elliot will make his test debut at Murrayfield after being bracketed with the 82-test veteran in the starting line-up.
Mealamu said he was relieved the penalty has been reduced after the panel of South African chairman Peter Ingwersen, Robert Williams (Wales) and Jean Noel Couraud of France agreed his actions were reckless rather than intentional.
"For me there's a lot of relief. It's been a tough sort of week having something like this hang over my head," he said.
"I've never, ever played the game to ever hurt anyone.
"To finally get this come through to say the way I did things was pretty reckless is a lot better than saying I intentionally tried to head butt someone.
"I feel a lot better and I'll take a lot more care the next time I do a clean out like that again."
Mealamu said he initially had no recollection of the incident and was surprised to learn he had been cited.
"The first I knew about the incident was when they said I was getting cited for it.
"It's hard trying to put it into context, it's something that happened just like that. It was two seconds in an 80 minute game. It's quite hard to comment on," he said.
All Blacks assistant coach Steve Hansen, who had earlier vowed Mealamu would be defended "to the death", was satisfied with the outcome.
"There was no intent to clash heads. For us that was the most important thing, to clear his name," Hansen said.
"Head butting intentionally is quite a huge act of foul play. He's not like that, we know he's not like that and that's why we've supported him so strongly. Reckless yes, but it certainly wasn't intentional."
Captain Richie McCaw, disappointed not to be able to share his record-equalling 92nd test appearance with a long-standing teammate, doubted the Mealamu saga would affect the All Blacks performance.
"It hasn't been too bad to be honest. We were aware the whole week he was going to be facing the judiciary. We planned for it.
"It's disappointing for Kevvy but for the team it hasn't been too bad."
He was confident Elliot would be up to the test after spending four previous tests on the bench.
"Hika's been planning to be playing. That's the way he's approached it. He's done a lot of the practice this week, he'll be feeling all right."
Meanwhile, McCaw denied the All Blacks were under undue pressure to protect their unbeaten record against the Scots.
"I don't really think of the history on that side of things. From our point of view he want to go through unbeaten, it's always the goal, we want to be able to perform this week, that's the motivation.
The Scots have gone 105 years without a victory over the All Blacks -- two draws in 1964 and 1983 are the only exceptions to 25 defeats.
Scotland's captain Mike Blair also said history was irrelevant.
"I think if we had been playing for 105 years and 27 games then it would play on your mind," he said.
"The past is past. We have watched Scotland matches against New Zealand on television but we are in a situation here of a unique team playing on a unique day.
"Obviously if we were to win the game, it would be something many a legend playing for Scotland hasn't done. There is history behind it but that isn't a motivating factor, we have enough of those."
