It would need to be a pretty damn big burrito inside an even larger box. You can check your local laws on regulation relating to the transport of live animals.
A quick search came up with (almost certainly out of date) federal regulations for the states, which... well, here:
Again, it's almost certainly out of date, but it gives you an idea.
Postal transport of live animals have their own rules and regulations, which will likely vary from country to country and region to region. Check with a lawyer or local transport service. The laws can and will be different wherever you are compared to wherever most everyone else is -- there's no general standard that I'm aware of.
Keeping the burrito in the box in place would likely be accomplished with some sort of packing filling. Bubblewrap, etc., with care taken so the smelly little menaces can't get at it and kill themselves eating it.
Insofar as etiquette goes, some
gods damned warning. If you're going to inflict thirty some hamsters on someone. Or less hamsters, really. More than one. Just one. Also please, for the love of all that is, make sure none of the damn things are pregnant before sending them. And send two burritos-inna-box, separated by gender, lest that status change mid transport.
Other etiquette... really probably depends on your relationship with the individual you're dumping the vermin on, and how much they actually want a multitude of the cursed beasts. Still, you are dropping something live in their lap, so something more personable than a letter or whatnot would likely be appropriate, if possible. Maybe a videogram or whatev', I'unno.