You don't need Patchou's permission to write a Tweak Plus! program, in the same way he didn't need MS's to write MSN Messenger Plus!
Also the kind of stuff you do in tweak Plus! is fairly mundane, and I can't really imagine Patchou objecting. Why not keep going with the project, keeping it active and then if Patchou has a serious problem with it (including some particular reason) then think about cancelling or changing it.