Please use question marks in your title in future. It can confuse people a little as they may mistake this thread for an actual guide/method.
As for decrypting and editing act.dat, for now it is not possible. No-one knows when you could do that because it's something that hasn't really been looked into.
However, you could possibly try building an act.dat from scratch using the recently-released act.dat generator script/app. (hard to link to it since I am typing from my Vita, but you'll see it.)
