To use a full length size die to neck size - Depends on the cartridge. If it has quite a bit of body taper, like a 30-30 or a 22 Hornet, then you just need to back off a full turn. Run your press ram up all the way, then screw down the sizing die until it touches the case holder. Back off 1 full turn and set the die. You will not push the shoulder back (or shouldn't unless there is excess head space) and barely touch the case body. If you have a chamber that is really big, you could back off two full turns. For a case with less body taper to it like an AI. There is very little body taper to it. You will squeeze the body down some, even if you back off 2 or 3 turns, but it will not bump back the shoulder.
When I use this method to size necks with, I try to have the expander ball "float" (with some dies you can do this with and some you can't). I do not tighten it up in the die and let it find the neck center when extracting it back out. Then it will expand with out pulling the neck out of center, keeping the neck as concentric as possible. Good Shooting and Good Luck.