I'm looking into making a Bard. While looking at subclasses in the 3rd party supplement Xanathar's Lost Notes to Everything Else, I found that the College of Discord subclass feature Melodic Mayhem allows the character to literally use an instrument as a weapon. This makes me have to ask (mostly for pure curiosity's sake), can there be an instrument with an attack bonus? I mean, is it possible for a DM to make (or allow a character to make) an instrument that has an attack bonus despite it being an instrument? How does that work with the rules?
To clarify, some weapons have text reading You gain a +X bonus to attack and damage rolls made with this magic weapon., so I'm wondering if an instrument can have this kind of modifier, since this Bard College can use instruments as literal weapons.