You can only try to override the whole beacons in your/the server's game.ini (a lot of work) or look for a mod to change the drops. but you cannot adjust only single things that you want have in the drops.
Overwriting the beacons always means that you have to write a correct list for your game.ini, that contains every possible loot for every beacon type including things like quality, blueprint chance or amount. Extinction Core allowes no acess to change things on the existing loot table.