It is very common in top tournament that a local celebrity or other people who like attention such as politicains, people from FIDE, etc, make the ceremonial first move. This is purely for the photographers, and of course it is perfectly fine to take back this move and make your own move.
In the game you mention however Aronian chose to stick with 1. e4 which is of course also an option. I don't think that Aronian was in any way influenced by the choice of Francesco Tristano, i.e. he would have played 1. e4 anyway.