ok. So I has a similar issue when I was younger.
Mum divorced when i was 3 Bio. dad had nothing to do with me.
Mum remarried I took on step dads name. I has everything - medicare, passport, tax, bank records, school records etc in my stepdads name since i was about 8. It took allot of paperwork to get my passport etc as I had to prove I had no contact with my bio dad. There is no way that he would sign over any rights to my step dad.
I went through the process of proving that I have no contact with him, that no one knows me in this name (stat decs, letters of acknodlgement etc) to get it changed.

If you can prove this and if need be to go through the court to prove this, i can't see any issues.

Got it all done now (though through my laziness it took me till i was 22) and name was changed.