Bookworm
good question, as a pilot, I would ask it I was to maintain 4000' or continue on the SID.
As an ATCO, I would hope I would be unambiguous; thus never causing any confusion and say something along the lines of "Fastair123, stop climb (or climb and maintain) altitude 4000ft"
If in doubt, ask, but I would say that even the first example cancels the SID clearance, but in this instance it would be worth checkng any ambiguity.