No. In an statement released to the press, ESRB president Patricia Vance said: "Manhunt 2's rating makes it unmistakable that the game is intended for an older audience. The unauthorized hacking into the code of this game doesn't change that basic fact. Parents need to be vigilant about monitoring what their children are downloading on the Internet and ensure that they are not making unauthorized and oftentimes illegal modifications to software and hardware that remove the controls the industry has so diligently put in place for their own protection."
The PSP isn't widely known for having the best security around, but it's clear that a bit more effort goes into unlocking the "unedited" version of Manhunt 2 as opposed to the PC version of Grand Theft Auto. "The Grand Theft Auto: San Andreas "Hot Coffee" situation involved a scene that was a) fully rendered in an unmodified form on the disc (the Hot Coffee mod did not alter the content that was there, it merely unlocked it), b) not previously disclosed to the ESRB during the rating process, and c) easily accessible to all owners of the PC version of the game. Conversely, in the case of Manhunt 2, a) content that was programmed to be part of the game (i.e., visual blurring effects of certain violent depictions) is being modified, b) the content was previously disclosed to the ESRB, and c) unauthorized versions of software and/or hardware are required to play the modified content."