It appears that the studio behind "The Hangover 2" didn't waste any time in replacing Mel Gibson's cameo role in the film. When Neeson was asked about the role, he was quoted in Variety as saying "I just got a call to do a one day shoot on 'Hangover 2' as a tattoo artist in Thailand, and that's all I know about it."
There is speculation that Neeson was recommended for the part by his "A-Team" costar Bradley Cooper; who is also a lead in "The Hangover" franchise. As the cast of the film has already proven they have a voice in who takes part in the project, it makes perfect sense that their input would be taken to heart.
I am very excited to see how Neeson plays the part. I have been a fan of his for years, and I look forward to seeing the final product.