This is an intentional misspelling on Kharms' part, as canpolat has shown an hour ago, but is not nonsensical at that. Since I happen to be familiar with Kharms' stories, I can infer what he wanted to achieve by writing эпиграммамы [epigramami] instead of эпиграммы [epigrami] (which is the correct plural dative).
Мамы in Russian happens to mean moms (declensed for dative case, to moms, but cases are of no other importance here than to explain the particular suffix -ы/-и/-i). What do moms have to do with epigrams? Nothing, almost. But the notion of moms, with its childish, giddy irreverence, does create a nice, jarring contrast with the exalted, if waggish, notion of epigrams. What can be nice about jarring contrast? Well, Kharms is sort of like Bukowski and the Marx Brothers at a Captain Beefheart & Zappa double tour. His stories are the trip the South Park kids sporting Che Guevara t-shirts took to the Mystery Science Theater 3000 with Orwell's and Kafka's books in their backpacks. Of course jarring contrast is nice, in Kharm's off-beat and subversive world. He was the archetype of the black sheep, a maverick amidst mavericks, a non-conformist par excellence. Inane as inane can be, yet more incisive and socially aware than (list your favorite heretics) combined. Of course his misspelling isn't guileless. He is taking a stand against the socially sanctioned conceptions about what is of value, which constitute the framework of pretty much any epigram.
The translation is wonderful. The translator chose to juxtapose the majesty of an epigram with everything redneck, as evoked by the phonetic chain "erp" in erpigram. That's the good translation at play. You don't translate just the words, and not even just the isolated meaning; you translate the culture.
Edit: And, I'm sure, Kharms actually valued the notion of the epigram. His whole opus, made of short stories, some super short, is nothing if not the wittiest of the epigrams. But, then, he decides to piss even on that. That's how he was.