Warning level is lowering automatically for several days by itself. No need of lowering it manually. If a user is not added to a special group, it has very temporary effect if to increase his warning level. You need to do it over and over again and again. Otherwise premoderation will overcome in several days by itself.
I know that the level is reduced automatically, what I meant is that if a particular user stops breaking the rules (that's why I said I doubt it) I could reduce it manually. I believe that everyone deserves a second chance, but that does not mean that we should leave a lot of time between doing one thing or another. You can see the proof in the number of users with many rule breaking posts now having their posts moderated.