Event troops for the North in winter/Winter Wolves

I thought it might be a cool idea if when harsh winter sets in to a province of northmen some event troops could spawn as a raiding party (probably along the lines of ironborn reavers) but you need to use it to raid/attack the south or you suffer penalties, as we are told that the North has historically used raiding and warfare to support itself during war and to reduce the burden on its food reserves (ie Cregan Stark's winter army during the Dance of Dragons, the greybeards of the hill clans under Stannis, to Jon and Alys's Karstark's discussion of old men going "hunting" in the winter - apparently volume I of Fire and Blood will also discuss this as a longstanding northern tradition that caused tension between the Starks and Targs when Aegon and his successors prevented what was essentially the way the north dealt with insufficient resources in winter). This mechanic would also reflect the fact that in harsh winter the northern peoples are at an advantage, creating a sort of don't invade Russia in winter scenario where if you have invaded the North as a Southron and winter has just started, on top of attrition the Northern army is suddenly 15% bigger.