Function CFAttributedStringReplaceString 

pub unsafe extern "C" fn CFAttributedStringReplaceString(
    aStr: CFMutableAttributedStringRef,
    range: CFRange,
    replacement: CFStringRef,
)

@function CFAttributedStringReplaceString Modifies the string for the attributed string, much like CFStringReplace(). It’s an error for range to specify characters outside the bounds of aStr.

(Note: This function is a convenience on CFAttributedStringGetMutableString(); however, until CFAttributedStringGetMutableString() is implemented, it remains the only way to edit the string of the attributed string.)