you could call the song "ar chnocáinín aerach ..." but "chnocáinín aerach" without a preceding preposition wouldnt be right. If Cill is lenited it would be because of being in genitive case, little hill OF Cill Mhuire.
example "coill Chill Mhuire" Kilmurry/Cill Mhuire wood , "Contae Chill Dara", County kildare/Cill Dara


http://www.ainm.ie/Bio.aspx?ID=310 -- biography of Seán O Cadhla, teacher, 1860-1942. His mother Máire Nic Chonmara was from Kilmurry, Co Clare and it's part of the family tradition that someone from their family composed 'Cnocáinín Aerach Chill Mhuire'