Yes, you can just take alternative routes, which include road walking, but they are not overly busy roads.
However, at Tyndrum I asked the tourist office about walking my dog across the next section to the Bridge of Orchy which I wasn't supposed to be able to do. They said as long as my dog was on the lead it would be ok. That morning I saw a farmer just as I set off and also asked him if it was ok. He was fine about it and just said it was irresponsible dog owners letting their dog run madly where there were sheep which was the problem.
So no problem.
Janice & Harlie(dog)