It was *never* possible - the only thing you were able to do before the serial number was properly protected was change it to hide from it, but it’s still there when it goes back to the real serial number.
It’s tied to the serial number of the Chromebook, so essentially the answer is no. In your case, you may need to wait until you graduate before they remove it. The problem is the may be a technicality where it has to have an enterprise enrollment lock attached to it due to some school district policy. If I was in your position (especially since your parents probably paid for it!) I'd tell them to keep the Chromebook, not get a cent for it and pound sand unless they sell it to me without a BS enterprise lock and give me the ownership information in case it was needed.
At this point, you need to remember to hold them to their part of the deal if you bought it and cannot rely on your parents to do so. They do not understand the problem, and will leave you dead in the water especially if you make your own money and it's old.