How to assign attributes to a group of planets?

Hi,

I'm a noob at Galaxy forge. I want to create a galaxy map that has a cluster of planets in the middle that are rich in artifacts and planet bonuses while the rest of the galaxy has none. The idea is pretty simple, its a bit like MOO as I can do in a map with no mod. Everyone is going to fight for that planet cluster.
How do I do this? Please help.

I didn't find the right solution from the Internet.

References:
forums.sdgfxfd.com/358477/galaxy-forge-how-to-assign
Sustainable Energy Video


Thanks