Africa Map with Random Merged Countries

1. First off, everything you want to be hidden by default needs a common class so we can use CSS to reference them all at once. For what you're doing, it seems "country" might be suitable since it's already there.
2. Second, use the CSS ".country{opacity:0}" to hide all countries by default. Just add this inside <style> tags to implement it.
3. Thirdly, use "random-svg-highlight" to show the countries again. The CSS for this is ".svg-holder .random-svg-highlight{fill:#ffff80;opacity:1}". This will override the first one and make any selected groups show up.

Let me know if you need elaboration anywhere :)

Then, you need to organise your groups in Step 2. The editor will show you the boundaries of each group, and you just need to put in groups of countries. It might be easiest to do this in a spreadsheet to maximise your number of groups (to give a large enough pool). Essentially you need to hard-code the groups themselves into Step 2, there's no way to tell the randomizer to pick "groups of countries" other than to group them manually and use "random group".