What about a modern performance of a shakespearean play could be changed without affecting the play's meaning?

We could change the language and adapt it to reflect the contemporary English we use nowadays. That would make the play more understandable, especially for the young people and wake up their interest for the theatre.  

We could change the setting, that is, time and place of some plays and adapt it to contemporary surroundings, without changing the topic of the plays, as Shakespearean problems and inner struggles are still present in the 21st century, only in different ways.

For example, we could change characters' professions or some circumstances without changing the plot of the story. Or, perhaps, try to represent some contemporary family issues, by readapting Hamlet into a boy who is fighting against his stepfather.

they are most likely about to fight in the battle of gaul