Carol, sorry to hear you are traveling in July. Yes, the theaters for the most part close from mid June through the end of August. This was pretty much common in the region and I am guessing where it has changed it has changed in response to tourism demands/opportunities. The summer break was probably due a little to getting ready for the next season and a little or a lot due to the fact there was no air conditioning.
If you get just a little lucky and if there is practice going on a the Opera House you might be able to enjoy a really great piece of sausage while listening to the music. Here is how it works: Facing the Opera House there is a street that runs up the right hand side. The street name is Hajo utca. At the back side of the Opera House it becomes pedestrian only. As you walk up the street you will see on the right a red storefront with the title Hus Hentesaru. I believe it just means Meat or Meat Market. In the small window you will see some great looking sausage. Go in and tell the big burly man "sausage" and hold up one finger for one piece. He will as something to the effect of "here" or "plate" to which you answer yes. Next question 'bread", answer, yes. Next question "mustard", oh heck yes. Now your turn to ask, say "Knife" and he will reach in a drawer and pull out a knife with a giant butcher knife handle but a blade that has been ground to a very small steak knife. Drinks are in the fridge behind you. Pay and walk to the table outside. There with some luck they will be practicing in the Opera house with the windows open (no A/C). You get opera and a really great piece of sausage. Or at least a really great piece of sausage and a great conversation in signal syllable words. Don't forget to return the knife. I think its Jewish owned as I have found them closed on the few Saturday's I have tried.