Coulter isn't specifically a Scots word. It is also found in England.

I googled it and got this

coul·ter (kltr)
n.
A blade or wheel attached to the beam of a plough that makes vertical cuts in the soil in advance of the ploughshare.
[Middle English culter, from Old English culter and Old French coltre, both from Latin culter, knife, ploughshare]

For all that, I take your point, Jim.

I have two rules of thumb I use about anglicising words:

1. Is there an exact or, at worst, a very close equivalent in standard English? If not, then leave the original alone.

2. If there is an equivalent in standard English, can it be used without destroying the rhythm of the words or in any other way adversely affecting the poetry of the song? Again, if the answer is no, then leave the original alone.

Most of the time, that means don't anglicise.