Big Mick:
Looking at that line, I strongly suspect it's not what the author must have actually written, because it doesn't scan. It's very easy for mistakes to creep in through the writing or the printing, so I think there's no duty to stick to a text that may have been corrupted, if it might make better sense with a little change:

If I were singing it (and if I had the tune, I think I would want to) I'd be inclined to turn the line to:

Now may it be our country's cause
Our party feelings blended
'Til lasting peace from equal laws
On both will have descended
'Til then the Orange Lily be
Your badge my patriot brother
It's the everlasting green for me
And we........for one another.

(Or maybe "Now may it be in common cause..." Either brings out the sense I think is actually intended.)

This is from the man who had the impertinence to rewrite and augment a Seamus Heaney song, "The Road to Derry" (and that's on my website as well. Frank Harte told me that Seamus quite approved of being included in the folk process, though I don't know what he thought of the amendments.)

I wonder if the song is related to "The Orange Lily-o", - which is another song you might think of bringing in to the repertoire. It's about a flower show, with "patriotic undertones" - and a hint of disdain for the English Viceroy, I think.

"Oh did you go to see the show
Each rose an pink a-dilly-o
To feast your eyes upon the prize
Won by the Orange Lily-o
The Viceroy there so debonair
Just like a daffy-dilly,O
And Lady Clarke, blithe as a lark,
Approached the Orange Lily,O
Then heigh-o the Lily,O,
The royal llyal Lily-o
Beneath the sky what flower can vie
With Ireland's Orange Lily,O

The elated muse, to hear the news
Jumped like a Connacht filly-o
As gossip fame did loud proclaim
The triumph of the Lily-o;

The lowland field may rose yield
Gay heaths the highland hilly-o
But high or low, noi flower can show
Like the glorious Orange Lily-o

The heigho the lily-o
The royal, loyal lily-o
There's not a flower in Erin's bower
Can match the Orange Lily-o

That is from, Colm O Lochlann's Irish Street Ballads - and on the next page there is Mrs McGrath. Colm writes in the notes about Mrs McGrath: "In the years 1913-16 it was the nost popular marching song of the Irish volunteers, Ilearnt it on route matches."

About the Orange Lily-o he writes "I heard an older and more pungent ballad, but could not find it printed. All I remember is
"Do you think that I would let, ---- Fenian ----
Destroy one flower of the Lily-o?"

The thing is, there's always been in principle an honoured place for the Orange tradition in Ireland. (That's why the tricolour looks the way it does, instead of the sectarian Green with Papal White and Yellow that it started with in 1916.)

Incidentally the tunes and metre of "The Sash" and "Kevin Barry" are interchangeable. And I think actually both songs work better if you switch the tunes around. If you've got the nerve...