I know there was something add to the NEC about the use of Christmas lights
year round for decorative lighting outdoors,so is string lighting considered as Christmas lights? I have a costumer that wants his building out lined with string lights I suggested belt lighting.
If the lights you are using are designed for permanent use then I don't see an issue. For that matter who is to say that xmas lights are only for xmas. If they are installed for permanent use then I am not sure 590.3 would apply.