A number of knots, seizings, soft eyes will suit, as will re-doing the splice, depending on your skill. But without seeing the eye you have and knowing the type of halyard
you are using, the types will vary. Shackling to shackles isn't the smartest option because it is metal-on-metal friction.
But the OPs question is about the bar which prevents the shackle tumbling. Despite the suggestions to punch it out, common for some shackles with a bar, it's not clear this bar is able to be punched out.
show only one hole. Punching that will just mash it. That suggests its been screwed in (good) or driven in once then the end pened out or welded in, which requires you to drill it out (pointless). Does the end in the whole have a hex/allen or driver type head