After 2-3 days of trying, the hack works fine. Except of some members complaining that the same message pops up everytime when they open a page. I guess this is a fault of the browsers they may be using since I've been trying the hack with IE6 and haven't seen any problem.
The only thing I'd like this hack to have, is "radio buttons for members". This way there can't be much abuse. For mods and admins I'd like it to be as it is, in cases they need to send the same message to more than one member.
P.S. I couldn't download the addon mod for cp