Not very knowledgeable myself, but I don't think you need to remove that to replace the tumbler. You do need a special tool to remove the metal ring around the lock on the dash though.

I was fooling around the ignition lock area because I was suspecting it as the culprit for my intermittent "crank but no start" and "no crank at all" problem. It turned out I was right. I had the lock changed, and never had a problem again since. One other symptom I noticed each time the intermittent problem occured, was that the climate control display wouldn't come on with the key turned to position 2.

I wouldn't leave the key in the ignition if I were you, but for other reasons. First, I don't think you can lock the car with the key in the lock, and second, doing that over an extended period would probably drain your battery, because as soon as you insert the keys, certain electronics are turned on in the background.