Most pipe band members I know do not speak of getting "costumed" up, they speak of "kilting up," which means dressing for the occasion. When we speak of details of what we're to be wearing at a certain type of performance, typical detail attends to type of shirt, hose, shoes, sporrans, in the "uniform" but never/rarely is the kilt mentioned. It's obviously a given (to be repetitively redundant) that the kilt will be worn.

There are a number of pipe bands out there with enough money from various sponsors and/or fundraising endeavors to spend on fancier dress. While some might well argue that all of that extra gear (doublets, crossbelts, ostrich feather hats) could be viewed as "costume," whether it looks like a costume or dress gear really depends on the deportment of the wearer(s).

Occasionally I will wear a kilt as part of an ensemble for a Hallowe'en or other costumed event. Then, I agree, the intent is clearly that it is part of a costume. Other times, when I've spent considerable time "getting it right" (as in a preparation for a Burns' Nicht Dinner), any suggestion that I'm costumed for such an event would most likely be met by the rejoinder, "I'm dressed for the occasion." More or less . . .

Mac