Can you talk to your parents about this? I know when I was about your age, my parents were in a massive upheaval of divorce, remarriage, and selling our home. I was 17 and leaving for college and basically felt homeless. That is a bit more extreme, but I feel like I understand where you are coming from. You are at the cusp of adulthood. A whole lot of things are going to change and you will be making a lot of big decisions about your life ahead.

Your parents changing your room without your oversight, opinion, or approval inplies a lack of sensitivity for your feelings, as well as a diminishing of your maturity. It is practically infantalizing.

Perhaps you could talk to them about it, by thanking them for the thoughtful gesture and also explaining how it bothers you for them to dictate your space to you at your age. You could tell them that you would like to be a part of the decision making process. It not only shows maturity and sensitivity on your part, but also acknowledges the good intentions they probably have in doing this for you.

On another note, I totally get that attachment to things from your past. I'm just a hair too organized to be a hoarder. It was indescribably hard for me to "lose" my home when my parents remarried and moved. I felt adrift and homeless for a very long time. It really is the little things that bring us comfort.