This is what I would do. First I would buy 222 Form/Trim die.
This is what I would do. First I would buy 222 brass......
Old Roper's method certainly will work, but seems to me to be extra work, and in my case, doing it his way would involve buying several dies and an extended shellholder that I don't have.
I looked at the link, the trim die requires an extended shellholder, and the form die is a separate die from the trim die. Also, to do it the way he would, I'd need to buy a .223 small base sizer die, which I don't have, and really don't know if it would be needed.
The OP didn't say what tools and dies he has, nor even mention what .222(s?) he would be using. He just asked if .223 could be re-worked into viable 222 Rem brass. To which I would say, "YES".
While I have never had the need or desire to perform that particular conversion, based on having formed .30-06 into .308 Win, 7.7mm Arisaka, and 8mm Mauser, I'm certain .223 to .222 can be done, done simply, and would produce "viable" cases.
All my case forming of the 06 brass was done on a single stage press (O frame, because that's what I have) and done using only the .308, 7.7 and 8mm FL sizer dies. Trimming was done on a Lyman case trimmer, and the formed brass works perfectly in my rifles.
I have two .222s, a Rem 600 and a T/C Contender, so I'm not be trying to feed a match gun with a super tight chamber. TO date, I've never needed a small base die for any of the rounds I reload, including .223 and .308 in semi autos.
Compared to forming '06 brass, .223 to .222 is moving less brass a shorter distance, so it shouldn't be a problem.