I don't necessarily agree that a manager can't change style. Non-league manager I know well went into a relegation-threatened club in the Jan a few years back. After assessing the squad (a few players had left with the managerial change as often happens in non-league) he set them up very defensively and very direct. It was boring, route 1 football. The fans hated it, calling him a cnut and "the non-league Sam Allardyce". It was effective though, and he kept them up with games to spare. The next season, he revamped the squad and played the way he wanted to, which was much more attractive and much more attacking. They had an excellent season and although he left eventually, he's still very popular at that club.
So, I don't see why someone like Rosenior can't adapt a bit become a bit more attacking.
Still does look like a bit odd in comparison to some of the other people that have been linked and a bit at odds with how the squad has been built. I said this some time ago, and I still think it's the case. He was the No. 1 target because of the PR value of bringing him in. When we first linked, his stock was high and a lot of people were talking about him. Landing someone with that kind of profile would have been a statement of intent.