EdoFede,
I bought a DS2072A-S (identical to non -S version, just has the builtin generator) a little over a year ago and did the upgrade at that time to 300MHz + All Options. I installed the newest firmware you just got from Rigol yesterday and and still have all options activated. The guide you linked to from earlier in the thread is the correct one, and you can uninstall all the options and bandwidth upgrade with a single command ":SYSTEM:OPTION:UNINSTALL" at any time. I have been playing around with the different codes recently and so have uninstalled, reinstalled, changed to different ones quite a few times over the last couple of months. As far as I know it does not matter what version of the firmware you have installed, the hack will work. Early on in the search for how to unlock the options you would have to have a specific firmware to do the unlock, but that was because it was the firmware itself that had been modified to allow the unlock to work, with the procedure you linked to that is no longer the case. You can install the new firmware, then do the hack. Or do the hack then install the new firmware, it doesn't really matter. When you do install new firmware upgrades you do not need to uninstall the hack first, you can do the upgrade with the hack in place. The procedure really is as simple as it sounds, I have not heard of anyone have problems with it. Go forth with confidence!
Hardware Ver: 2.0
Software Ver: 00.03.04.02.01 AKA 00.03.04SP2
Edit: Corrected rigol model I own.
Edit 2: Wanted to add that Rigol have been aware of the "upgradeability" of their scopes for a long time now, if they wanted to stop it I'm sure they would have by now. Or at least patched the hole that allows it to work, but they have not.