If you really have no inkling about Scottish accents (and there are various distinct Scottish accents) you'll just make a fool of yourself if you try to fake it. Much better to sing in something close to your own accent. You can tweak some of the words to help the rhymes along if you like, that can sound OK and avoids drawing attention to the fact that it's a "translation".

Even Scots people who exaggerate the accent and dialect in an attempt to sing in a broad Scots which is totally different from their everyday speech can sound contrived and uncomfortable. If you're not Scottish, don't even think about it.

Some of the old ballads exist in English and in Scots variants, so it may still be reasonably authentic to sing them in a non-Scots accent.

Marje