Is it possible to add a pop-up notification when contact change his status (like phoenix plug-in)?
It's already available when contact goes online/offline so it's simple to add, I guess
You can do this with individual contacts by doing this:
Right clicking their name
go to Messenger Plus! Extras
Notifications...
then you can configure it however you want... This only works with individual contacts so far (that I know of). But I'm sure if there was enough demand Patchou could add a feature allowing you to do that with all the contacts.