Malcom Macfarlane did indeed set Maclean's to music AND he composed Gaelic lyrics for the song. It was recorded by "celebrated Gaelic tenor" Sgt-Major Colin Macleod

aources - World Heritage Encylopedia, Wikipedia, [uk]National Archives

"'Nurse Cavell Lament. Words by Murdoch Maclean. Music by Malcolm Macfarlane. Edited and arranged by Arthur W Marchant, Gaelic and English words. All profits for the 'Scottish Edith Cavell Fund'. Sung by Sergt. -Major Colin Macleod, celebrated Gaelic tenor. Dedicated with permission to the Heroine's Mother, Mrs L S Cavell'
Recording is held by the Royal London Hospital Archives and Museum

Malcolm Macfarlane also composed lyrics Mo Dhachaidh to an existing air.