What are reasonable alternatives to changing your name for academic publishing when you have a common surname?
In terms of publishing papers, I'm not aware of any requirement to use your legal name. A common example would be those who continue to use their maiden name (where people change their name on marriage). A friend of mine did the reverse, and wrote her first paper under the name she would assume when she married shortly afterwards.

The trickier case is what will appear on your PhD. It may not matter much, but it would probably make life easier if that said the same as your papers. You'd have to talk to your university about their rules.