Josh Bayliss and the suspended Grant Gilchrist will return to their clubs.
Gilchrist, who was red-carded in the defeat by France, is banned for the rest of the championship and Edinburgh's match with Connacht.
Scotland have two wins, while Ireland have won three out of three.
Thirty-two times capped tighthead Berghan, 32, featured as a replacement in the championship opener against England, while fellow Glasgow forward Cummings, 26, is yet to feature in the tournament.
Cummings, capped 23 times, strengthens the lock options in Gilchrist's absence, with the Edinburgh man having taken his tally of international caps to 62 by starting against England, Wales and France.
Glasgow flanker Darge, 23, could make his first championship appearance, while club-mate McDowall, 25, may make his international debut at centre.
Bath flanker Bayliss, 25, did not add to his two caps over the first three rounds.