Have a bucket ready as well...
Cut the piping almost all the way through and then place the bucket underneath...
Then cut the bottom of the 1/2" pipe through, remove the cutters, and hold the bucket over the stub...
The pipe should "snap" off with a little wiggle and the water should not make too much of a mess...
Takes a bit of practice but once you have the knack for doing it you can be quite quick and neat...
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And be careful... the inside edge of the pipe will be very sharp - do NOT try to stem the flow of water with your thumb (I speak from painful experience)...
The angle stop can be placed on the pipe before the water has stopped flowing out...
Ensure you have placed the escutcheon on the pipe and that the angle stop is already closed or you can get a bit of a geyser...LOL
If the escutcheon is difficult to place on the pipe, put it on backwards and wiggle it a bit then turn it around - it will loosen the small "fingers" inside a little bit to allow it to slide over the pipe end easier...