Demand a change for Self Expression!

My son is in 7th Grade he makes good grades and is involved in other activities at school. He is being forced to cut his hair because it is not "dress code". He has been growing his hair and donating it in his dad's honor since 2014 when his father passed away in a car accident, his father used to donate his hair as well. After his father passed he made a promise to continue doing this. I recieved a call from the principal which I have had a previous conversation with at the beginning of the year with explaining his hair and he never followed up with me until today he told me very clearly I have until Monday which is less then a week away, to cut his hair or he would place my child in ISS. This doesn't seem fair to me I feel like I am punishing my child for trying to do something good. What good will it do to place my child in ISS where he will not have teachers to teach him, how is his hair affecting others around him? I also don't understand why we live in a world where we are being told it is ok to be who you truly feel you are as far as gender is concerned and equal rights for example how is it ok for my daughter to have her hair to the floor if she chooses but not my son? My daughter is allowed to wear her earrings but it is not allowed for a boy to wear them? I understand dress code to an extent but I also firmly believe some things in our dress code need to be changed. I asked how long has it been since it has been updated and with quick response the principal answered it was updated this year. So I then asked what were the updates his response was nothing except kids can't wear jeans with holes in them. I then asked how long has it been since the rules on hair has changed and he could not answer that. Well my only response for that is maybe that needs to change.