BIOMUTANT How to Get All Tribe Weapons and Armor

It is possible to switch tribes to any other tribe you aren’t at war with. So if you join the Jagni initially you’ll be at war with the Myriad they won’t allow you to join, but you can join other tribes since you aren’t at war with them.

Start out with any tribe you’d like and conquer two rival outposts to get your tribes weapon and armor. After this go to a different tribe you aren’t at war with and join them. Conquer two outputs again to gain the rewards, then switch to yet another tribe. This can be done for all rewards and at the end of it you can rejoin your old tribe, because they don’t mind that you stabbed them in the back earlier.
And its that simple (albeit time consuming) to get all tribe weapons and armor.

To join a tribe go to their main outpost (indicated on the map with a large insignia that is brown/goldish with green on top) and ask for the sifu.
Do note that tribes are either light or dark which has consequences for the ending. The three light tribes want to safe the tree of life while the three dark tribes want to destroy it. If you change tribe from light to dark (or vice versa), you will get a different ending if you stick with that tribe.