In most cases, using accents that are not your own is totally unnecessary and often detrimental to your being involved in the song - how do you relate to your voice if it is not your own?
If you if you sing say Scots or Irish songs to audiences from those places they can and usually do sound risible and you can become a figure of fun.
If you want to study an accent to acquire it, fine, but it hardly seems worth the trouble.
Most of these songs translate perfectly into your own chosen mode of expression (singers more often than not sing folk songs in a neutral version of their own accent - not broad Liverpool or Birmingham or Cockney, in which the songs would sound just as ridiculous.
The problems arise not so much with accents but with with dialect words, then you have to choose whether to use them anyway or to change them altogether.
If the song is based on dialect you have a choice - to sing or not sing.
Personally I choose not to, as much as I might like to.
I love Scots songs, particularly the ballads, and have managed to include about forty of them in my repertoire by slightly adapting them - I'd like to have learned more but I didn't because when I tried I couldn't get them to work for me because they sounded phony
I have never understood a Scots singer with a beautiful Scots accent singing a Scots ballad in a phony, mid-Atlantic American accent - talk about throwing away a natural gift.
Jim Carroll