Yup, if you're a Mac user, you're out of luck for a lot of the little utilities that make life easier for Poser users.

Magnets or trying to find an existing t-shirt with breast morphs might be your best bet. Or you could use dynamic clothes. If you're doing animation anyway, dynamic clothing should be easy.

I don't think you're allowed to send the P4 nude woman or her clothes to anyone. The Poser license does not allow it. However, anyone who has Poser has those items, and could make the adjustments.

I think they could send you the CR2 of the t-shirt, as long as they don't send the OBJ as well. If I'm wrong, I'm sure someone will correct me.