If I am correct, you must be a GM to lead a Wiki team. He works well as the leader of the Wiki team.
Was one mistake. Literally, one mistake. Should it be completely ignored? No. Though it shouldn't mean he should fail his trial, if anything he should be sat down with and lead through all of the commands to assure the fact it doesn't happen again. As said, Tahmas didn't realize what the command did, if he was told and explained about the command he wouldn't have used it. There was a lack of knowledge on the material, that is not his fault. He should've been prepped better, which still can be done through his trial.
If I understood it right, it was through an alt account(?). If I did understand it correctly, that isn't Tahmas' fault either. He was unaware of who the player was, Tahmas thought he was helping that was all. If there is to be a punishment for this, the superiors above him will deal with/punish him. As of why I am defending him, its because from what I know and have seen he has been a fully competent leader of the Wiki team. Along with the fact he has helped the server quite a bit.
As said previously, he wasn't aware of the commands because the staff in charge of him did not explain it to him. That is not his fault.
Another thing I want to understand, I still do not see why you want Tahmas to ultimately fail his trial. It was a single mistake he can learn from, not to mention it was something that had to be dealt with at one point. Another GM could've ended up going down the same road, used the command and ended up clearing the inventory of the players. The command needed to be removed from being used by GMs, someone had to discover it at one point, it just happened to be Tahmas. Though you seem to have something against Tahmas being a GM as a whole. If anything you seemed upset/triggered by the fact he was able to earn a Trial GM title so quickly. From all of your comments, it always rounds back to a "he was rushed into a trial" or(and I quote) "I think people are forgetting how rushed Tahmas Trial was,". His trial has yet to end and by the end his position in staff will be chosen. Nothing is set in stone yet, its still a trial that can be denied in the end.
Though in all, this was a mistake that anyone that wasn't given the right knowledge could have made. Anyone. Hes human, you're human, I'm human. The GM's and staff of this server are humans too, they're not immune to human flaws. So as I said, its best to move on after these mistakes are made and forgive what happened.