Yes, formal is the normal, informal is only between people who know each other. If you are a native, then a young person addressing anybody older in the informal way is a sign of huge lack of respect, borderline insult.

But you are a tourists, so it doesnt matter the slightest bit.

As my teacher used to say - "we did not herd geese together, so that (s)he can talk to me this way/informal".

(Nem őriztünk együtt libát, hogy ilyen hangnemben beszéljen velem)

It's not clear how fluent you are...if you aren't fluent enough that it will be obvious Hungarian is not your mother tongue, I cannot imagine any but the most hardened of souls will not give you a pass.

I'm getting the sense you may be pretty fluent. If so, I know you may want to let on that you are a local and blend in as such, but to be safe, why not purposely indicate you are a Hungarian born abroad and not comfortable speaking in the formal? I think anyone but the most grumpy of pensioners (and there are some of those whom you will never make happy) will accommodate.

Finally, remember you'll never speak to most of these people again. Get there and and experiment. Try to start out with younger/middle aged folks and/or shopkeepers where you are the customer - both of who will be more forgiving. See how they respond. If you offend someone, so what. It won't be the first, nor the last, but may indicate next time to give more warning.

Thanks for all of the great advice ! I'm sure that it will be totally obvious that I am not a native speaker since in the U.S. we tend to "Americanize" our Hungarian. Meaning that if we can't think of the Hungarian word for something or if there isn't one, we just use an English word and tack a Hungarian ending onto it. I figure I'll just put it out there and hope that in Hungary they will cut me some slack knowing that I'm not a native speaker but trying to do my best !

I dont want to sound arrogant, but there are words for everything in hungarian. This is an inherent trait of agglutinating languages, they can form words for every need, from already existing parts.

Mimi, don't let rawlee intimidate you. I year all kinds of English interspersed in hungarian. And my wife loves the Hungarian equivalent of spanglish.. For instance our sons are the "boycos."

Ha ! That's funny ! That's exactly what I am talking about ! I suppose, over time we get lazy or just forget what the word is for lack of use. For instance, my mother who is now 90 and came to the U.S. at age 37 could not remember the word for appointments so it became "appointmentok". Another is the word for microwave. There was no such thing back in the late 50's when my parents left Hungary so we don't know that word, although I'm certain there is one! I'm working on expanding my vocabulary before our trip ! Thanks for the encouragement !

Appointment is "időpont", microwave is "mikrohullám" (microwave oven is "mikrohullámú sütő").

Thank you ! Much appreciated ! I will add those words to my growing vocabulary list !