thing is - if he's hiding his Romulan nature - why would he alter his ears with a blunt knife rather than getting 24th century technology to do it?
Maybe because he'd be making a statement with it. Getting an unnoticeable surgical alteration doesn't make any statement about rejecting his true nature. People have to see it and know you did it yourself.
Plus it just makes him look hardcore (which is probably the true motivation behind the choice of his ear being mutilated in the film, but I just like to look for a deeper meaning).