Fine his parents $100, expel him from regular class for a week and have him do homework in a separate room by himself. Parents will scold him, he has to pay a price that actually registers. (at 14 I'm more concerned with losing 2 weeks of Xbox than a felony legal status I don't fully appreciate). He'll probably not do it again, or maybe he will, who cares, unless he escalates it's fine. That's just kids being dumb, and at age 17 it's not even interesting anymore.
I mean jeez, a felony? Give me a break. Kid changed a freaking wall paper. If he had done that 50 times in a row, you still don't give a felony, that's ridiculous and carries extremely heavy consequences.
I mean, for god's sake, there is a professional apartheid system. You have a felony? You get discriminated, for a job, for access to uni, for access to housing etc etc. It's discrimination, period. Why do we relegate 14 year old's to that position for changing a wallpaper in a prank, even if he did it 10 times?
The only reason this discrimination of people with a felony makes sense, is if we put the label of felony only on people who ought to be discriminated against. i.e. similarly to how if you molest a child, you're labelled a child molester and get discriminated against if you want to work at a school, with few exceptions this is usually a very sensible thing to do. But when we give a label (including the burden of the discrimination affecting people with a felony) to a 14 year old prankster, we can't justify it.
History is full of people who have lived wonderful, moral, lives, who made great contributions to society and went on to be upstanding citizens, who pranked way worse. You really think these people ought to have been given felonies, too?
There's a ton of iterative steps both in punishment and prevention. It usually starts with targeting parents, with council from people a kid looks up to (i.e. not the principal), with luxuries like games being taken away etc. Really I don't get it, changing a wallpaper on a computer is like pulling your kid brothers' hair, it's not something the police has to get involved in. It's a parenting/school type issue, not a criminal one.
If sensitive info was on the computer, sorry but it's not very relevant. 1) Someone do your job, you get paid for security or have security responsibilities that get wasted by a 14 year old. 2) How should the kid know, he didn't even touch or target it. If we start punishing people for what they 'might' have done, oh boy... talk about Orwellian thought crimes, it's beyond ridiculous. We can convict anyone of anything the moment the show the slightest intention to pull a prank.