I've cut off portions and reworked a number of time. Run lifeline just about portion you'll be removing. Snip a st about 1" in from selvage edge, unweave that row, working left and/or right, and everything below it will come off in one piece. AS YOU UNWEAVE, depending on how defined the sts are (if done a year ago they may withstand the picking process w/o being picked up immediately), you can pick up the live sts on a circ so you're ready to go. This works easy enough on st st and ribbing. Haven't done it on other st patterns.
Who's wearing a sweater that once had sleeves that turned out too short but I removed the ribbing, reworked them. Turned out to be a blessing in disguise because by redoing them, I did a tubular BO which gave a much nicer edge than the orig CO.
Keeping to the knitting basics