Pranks -- practical jokes -- are probably as old as Man himself. Or maybe older; it's hard to say, considering that whoopie cushions don't fossilize well. In any case, it's pretty clear that mischief-makers can and do make use of whatever technology is readily available. Which begs the question, what about transformation tech?

Sadly, the essential nature of practical jokes suggests that transformations won't be part of any gag for a good long time -- if ever. A prank is a contrived situation which is intended to make its victim look like a bit of a fool; it's not supposed to significantly alter the victim's body (just their dignity), nor is it supposed to have any kind of lasting effect on the victim (other than, perhaps, their reputation in their community). As well, it's worth noting that most people don't regard pranks as high-priority items in their household budget, so the tools and materials required to make a prank happen are almost certainly going to fall into one of two classes: Either they're the kinds of stuff which everybody has lying around the house, just because, or they're readily available in stores at low prices.

No significant alteration of the victim's body: Getting ink on their hands is one thing, but replacing those hands with paws or talons is something else entirely! At the very least, you're going to need transformation tech whose effects are readily reversible at any time. Spending a few minutes as a rabbit, that's a prank; being stuck as a rabbit for a few weeks or months or year, now that is a major change of lifestyle!

The "readily available tools" clause doesn't help much, either. It's be nice to think of... oh... a joy-buzzer-like gadget which turns people into anthropomorphic weasels, or back, on contact. But gadgets like that don't even exist! And if somebody managed to invent one, it sure as Hell wouldn't be cheap or ubiquitous. In a story, of course, the author can always get around logistical practicalities by simply declaring the protagonist to have stumbled across whatever-it-is by pure chance. But for us poor bastards stuck in the Real World, things are rather more difficult...

It would be interesting to speculate about the sort of world/society for which pranks could reasonably involve transformations. Since the vast majority of people are basically happy with the bodies they've got, it's very unlikely that there will be any tech whose raison d' être is to zap people into different forms. Whatever tech is used for the purpose, I'd be willing to bet that 'inducing transformations' is not its intended design function, but is, rather, merely one of the less-obvious purposes the tech can be used for. An obvious candidate: A medical device which is capable of detecting and treating a wide variety of conditions, even unto performing surgery and beyond. Such devices are reasonably common in science fiction, and they have a name: "Autodoc".

So let's assume a society in which autodocs fit the criteria for prankable tech -- they're everywhere, and it costs very little to use one. In such a society, everybody is going to be in perfect health at all times, up until the moment of their death. There will of course be other consequences (average life span is going to be way up, for instance), but 'perfect health' is the one on which I'm going to hang a practical joke. The victim gets up; goes to work as usual; at some point, one of his friends surreptitiously sprays him with a dose of something that makes him sneeze. Great (the victim thinks). I've picked up some kind of crud, cold or flu or whatever. Not a problem, that's why God invented the autodoc. So the victim uses the company autodoc, little suspecting that the machine's programming has been tweaked to give them very special treatment indeed... and when they're done, they've got pointy ears and a fine new coat of fur.