You can't.
You can't join team rocket in Pokemon diamond. Actually team rocket is not on the game
No
You can't join
in the doom room controlled by team rocket
no it can't that's why team glatic is in it.
you can't
You may not join Team Galactic in Pokemon Pearl or Diamond.
you can appear as if you have joined them at a point in the game going to the radio station in golden rod city, but you can not join them, (also the man find out you are not team rocket and battles you). so no you cannot become a member of team rocket.
you cant, AVADA KADEVARA, HA.
no you don't team rocket only gets one Pokemon from the boss and its not rare the boss keeps the rare ones
you have to go to goldenrod city and go underground. there will be a man from team rocket. walk past him and listen to what he says. then, he will think that you want to join team rocket so he will give you the outfit
You have to get the golden trainers card or if you have an action replay you can search up a cheat.