A comparison might be drawn here to the Coppers' Sweet Lovely Nancy, stanza 2:

When I am far across the sea
And you know not where I am
Kind letters I will write to you
From every foreign land

I have known singers who used 'thee' instead of 'you' at end of line 2, thus getting an extra rhyme. But that is not how the Coppers sing it so I always sing it the way they do ~~ it's their song. But no harm really done by those who do emend it to 'thee' if it makes them feel more comfortable with it, surely?

~Michael~