Paddy Jack, the Hackler, has fallen on hard times since the Sergeant was assigned Grouse Hall. He jails people on false charges, including drinking, for which he jails the Hackler. But soon Home Rule will sack "Old Balfour's pack"
"The hackler was a distiller of high quality Poitin in 19th century Ireland" (source: Hearing before Trademark Trial and Appeal Board, US Patent and Trademark Office, January 6, 2000 in re United Distillers plc "On December 16, 1996 United Distillers plc filed an intent-to-use application to register the mark HACKLER on the Principal Register for 'alcoholic beverages, namely, distilled spirits, except Scotch whisky, and liqueurs.'....)
Apparently the more common definition is "one that hackles [to chop up or chop off roughly]; esp: a worker who hackles hemp, flax, or broomcorn." (source: _Webster's Third New International Dictionary of the English Language Unabridged_, 1976); its this last definition that OLochlainn follows.
OLochlainn notes to "The Hackler from Grouse Hall" and its answer, "The Sergeant's Lamentation," explain the Sergeant's deeds and the references to people named in both songs and happenings in County Cavan. His source for notes is the singer.
The occurrences appear to be during Arthur Balfour's tour as Chief Secretary of Ireland in the late 1880s [1887-1891; his repressive methods earned him the nickname "Bloody Balfour." He made something of a habit of taking political prisoners -- see Robert Kee, _The Bold Fenian Men_, being Volume III of _The Green Flag_, p. 111 - RBW]. See for example the reference to the 1888 imprisonment of Father McFadden of Donegal in Derry Prison "for an agrarian speech" (source: Chapters of Dublin History site, _Letters and Leaders of my Day_ Chapter XXII "Parnellism and Crime" (1887-8), by T.M. Healy). I'd guess, no doubt naively, that the issue here is moonshining to defeat high alcohol taxation. - BS
The other possibility for the date is 1902-1905, when Balfour was prime minister in succession to his uncle Lord Salisbury. Gladstone's proposals for Irish Home Rule had of course failed, but the issue never really went away, and the Liberals were increasingly in favor of it in the early twentieth century.
Supporting this dating is the fact that, during the Balfour administration, there was a movement for "tariff reform" -- i.e. lowering of duties within the British Empire, which would have made it easier for the Irish to export to England.
Balfour tried to calm the tariff controversy, but succeeded mostly in turning his party purely protectionist, thus making the Liberals even more popular with the Irish, since they were more likely to favor both Home Rule and Free Trade. So the song might well look forward to the 1906 election which shunted the Conservatives from power. - RBW