"In this case it comes from 'pocán'(pron. 'puckawn'), the Irish for a billy goat."

Perhaps a pun, then, a double meaning? I was interpreting it as "puka" based on the lines:

"We've passed our Headquarters.
There my old ancestors always have been.
Let's come back again and we'll take up our lodgings
With the colleen-na-Gour where there's plenty of poteen."

When I heard the goat speaking, my heart commenced beating.
Says I, "'Tis a spirit called Petticoat Loose,
Or something or other that has come into Kerry."
And I thought to myself, I am done wearing shoes!

Generally not the behaviour of an ordinary, mortal, pocán, no matter what language you speak!

Which leads to some folkloric questions: Who is this "Spirit called Petticoat Loose"? And what does it have to do with the wearing of shoes?

(Though it seems the poor narrator of this story has already lost his shoes [or never had any on to begin with] since: "The fishes they ate all the nails from my toes" [and with those toes in salt water, too! :::Wince!!:::])

I also have some historical-folklorical question: are the lines:

"This darling old hero was raised in the mountains.
In the year '64, he learned some drill,
And some of his comrades I'm told are transported,
And now he's determined some blood for to spill"

and:

"Just outside the town he - (? my guess is 'butted' ?) some Highlanders.
With his horns he tore up their bally old cloaks.
The Highlanders bawled and roared melee murder,
Calling the Peelers to - (? 'take', 'lead' ?) him to jail"

refer to a particular conflict in history, and can this song be considered a political satire of sorts?

My guess is that, if so, this is an Irish Nationalist song, with the Highlanders being Scottish soldiers -- who once had fought against England for their independance and are now fighting for England.... But that is just a guess. I don't know for sure.