Merging badges:
This will be a lot easier when bulk actions are built out (in the works, we’ve been told) for the User Overview. But currently you can only apply a custom role.
Another current challenge is you can’t export users who have received a specific badge, although you can filter by that on the User Overview. So I’d recommend requesting the list from Support and/or asking support to help you with this.
It should be a lot easier in the future (filter on User Overview, then use a bulk action to apply the new badge to them and/or remove old badges). But we’re still waiting for those improvements (some research was done in recent months, so you’d hope it’s on the roadmap; check with your CSM for estimated timeline)
Splitting badges:
Similar answer here, although it’ll be tough to identify your criteria. I recommend checking with support on this one too. Generally, they’re pretty helpful with these types of requests. All of these things are fairly easy via the API, it’s just difficult/impossible to export the data needed (plus waiting on bulk actions)