Yes, but why would you? Adjustable stoker stems are boat anchors, and even at the minimum length are longer than most stems.
If you need a stem longer than 140mm, the bike may well not fit to start.
And if adjustability is the point, there are adjustable stems that would be better designed to do the job.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.