Seoirse has 'liomsa' wherever the text gives 'liom'. There is no great difference in meaning; liomsa is more emphatic. You'll have to decide which fits the phrasing better. Remember if you have a line with two a's together, such as "B'fhearr liom-sa an gabha..." , you are likely to from a contraction and only pronounce one a sound.

Seoirse begins the chorus: "Nuair a bhogfas tusa, bogfaidh mise, ..." Otherwise it's the same, but there should be an accent on "álainn"

There are spelling, grammar and punctuation errors in the above transcription. I hope I don't also make some in the corrections(The original may well come from that Clannad site!)
verse2: Bfhearr = B'fhearr , gabha' tá = gabha 'tá, an t-ord = an oird, dolfadh dtí au tabhaime e.= a d'ólfadh i dtigh a' tábhairne í
verse 3: Bfhearr = B'fhearr, h-aerach = haerach (differences in punctuation, not in sound) (Seoirse has "Bh'fearr liom-sa an feirmeoir 'tá seoladh amach go haerach". also he has 'oibir' but I think 'obair' is okay - you'll have to listen to see which pronunciation Clannad uses), dheas = deas,an chreafóg = na créafóig
verse 4: the 'o' before oíche should have an accent, ó