Whoops...double posting...
Okay, I'm back, and from what my ears tell me and what the DT database says, the Chieftains' version seems to change in the third line of the stanza...
Deck the halls with boughs of holly 'Tis the season to be jolly (Don we now) our gay apparel Troll the ancient Yuletide carol
Fast away the old year passes. Hail the new ye lads and lasses (Sing we joyous) all together. Heedless of the wind and weather.
The stuff in ( ) is what changes... sorry to let you down, but I can't make out what they're singing here...
^_^ cleod