Ok...
So i was 5 when my step dad came onto the scene.
From the age of about 9 i started using his name instead of my biological dad. My step dad was still able to sign my forms for school etc etc etc.
My dad wouldn't sign papers for me to legally change my name so according to BDMs I was still going by my biologically dads name until i was 18 when i was able to change it without his signature (which I did).

I did have trouble getting my passport and medicare card etc etc because I was using my step dads name and not my biological dads name because I only had my birth certificate in my old name and EVERYTHING else was in my new name, including my school records, bank records, tax records everything. I had to provided stat decs etc to say that the two names were actually the same person. Now, having changed my name it makes it easier as i don't have to provide ID in my old name.

So I guess my advice would be to weigh up how much trouble it could cause and how what it means and takes for you to change it.

Good luck with it.
Hugs
Xx