Learn English – Dull as ditchwater (not dishwater) … specific questions thereon

I'd call such a packaged (typically derogatory) name an epithet.

Merriam-Webster's definition of epithet:

A word or phrase that describes a person or thing

An offensive word or name that is used as a way of abusing or insulting someone

From Wikipedia's article on epithet:

An epithet, is a byname or a descriptive term (word or phrase), accompanying or occurring in place of a name and having entered common usage. It can be described as a glorified ... In contemporary usage, epithet often refers to an abusive, defamatory, or derogatory phrase, such as a racial epithet.

From Robert A. Harris' "Handbook of Rhetorical Devices" (page 6)

Epithet is an adjective or adjective phrase appropriately qualifying a subject (noun) by naming a key or important characteristic of the subject, as in "laughing happiness," "sneering contempt," "untroubled sleep," "peaceful dawn," and "lifegiving water." Sometimes a metaphorical epithet will be good to use, as in "lazy road," "tired landscape," "smirking billboards," "anxious apple." Aptness and brilliant effectiveness are the key considerations in choosing epithets. Be fresh, seek striking images, pay attention to connotative value.

A transferred epithet is an adjective modifying a noun which it does not normally modify, but which makes figurative sense:

At length I heard a ragged noise and mirth of thieves and murderers .... --George Herbert

Blind mouths! that scarce themselves know how to hold / A sheep hook ... --John Milton

In an age of pressurized happiness, we sometimes grow insensitive to subtle joys.

The striking and unusual quality of the transferred epithet calls attention to it, and it can therefore be used to introduce emphatically an idea you plan to develop. The phrase will stay with the reader, so there is no need to repeat it, for that would make it too obviously rhetorical and even a little annoying. Thus, if you introduce the phrase, "diluted electricity," your subsequent development ought to return to more mundane synonyms, such as "low voltage," "brownouts," and so forth. It may be best to save your transferred epithet for a space near the conclusion of the discussion where it will be not only clearer (as a synonym for previously stated and clearly understandable terms) but more effective, as a kind of final, quintessential, and yet novel conceptualization of the issue. The reader will love it.

Figurative Meaning

According to the website Words and Phrases from the Past the expression means

• a valuable hint (to tell or give information)

It matches the third example

Look here, you naturalist, and I'll put a wrinkle on your horn [I'll give you a hint]. Yonder hangs a magnificent bunch of fruit that I very much desire to possess

A second variation I found was "Well, that's a new wrinkle in my horn"

We love to get comments about the column. If the readers have heard the expressions that we share they tell us so. But if they haven't, we are sometimes answered with, "Well, that's a new wrinkle in my horn."

• Which is self-explanatory, a sort of I learnt something new today, something else to add to my collection, a novel thought. This fits quite well with the second quote

Let some respectable citizens, gen'lemen, come and take my last dying confession. It'll put a wrinkle or two in their horns, I'll warrant them !

i.e It will surprise/shock them = something new.

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Online Etymology Dictionary reports,

wrinkle (n.)[...]that of "idea, device, notion" (especially a new one) is from 1817.

Why Wrinkles?

From a book entitled Ellis's Husbandry: Abridged and Methodized (1772) there is the following excerpt which confirms @josh61 answer that farmers read the wrinkles on cow horns in order to guess their age, just as many do with the rings on a tree trunk.

This is a surer sign than the wrinkles in a cow's horn, by which we guess at their age; because they seldom have more than one wrinkle or circle, till five years old, and that sooner or later, according to the time of her calving; but an oak, ash, fir, hazel, and most other woods, shew these marks at three or four years old, when they are about the bigness of one's thumb

Here is an excerpt from the Australian Enquiry Book (1897) by Mrs Lance Rawson

To tell the Age of a Cow
At two years of age you will find a wrinkle at the base of the cow's horns, but it is >not fully developed till she turns three. When five years old another wrinkle will form, and after five she will get a new one each year of her life.

Every time you learn something new your brain wrinkles

There is the myth that the brain forms new wrinkles every time new information is stored. Many believe that the more wrinkles the human brain has, the more intelligent that person is. It's only recently that science has proven false that conviction, but it is one that still persists even today, like a popular old wive's tale.

Q. What do brain wrinkles have to do with how smart you are?

A. A lot of wrinkles seems to have more to do with what makes humans smarter than lower animals than with what might have made Einstein smarter than you. [...] Human intelligence appears to be related to the branching of brain cells and the formation of complex links between them, not the shape of the platform where the links take place.

I manage to unearth a very early reference that confirmed people believed every new wrinkle represented a new understanding; this folklore predates Etymonline's estimation by a sizeable ninety-three years, and is found in Jonathan Swift's tale The Wonderful Wonder of Wonders, written in 1720

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Earlier Example of the Idiom

The earliest written example that combined the words new, wrinkle, and horn is in The Medico-chirurgical Review, 1830, New York

Note the variation, to add a wrinkle to the horn (of knowledge)