An old salt (Experienced sailor) once told me "Never put anything on the end of a sheet or halyard that you don't want slapping you in the face."
Clap a whipping on the line an inch above the splice. Cut the shackle off. Use a bowline. Problem solved.
Seriously. A metal shackle on the end of a sheet or halyard can inflict serious damage on a sailor who lets the end get away from him. The weight of that shackle in the clew of a flogging headsail could mean death or serious injury to the foredeck crew.