As you travel the universe, you will gain access to new tech, meet new races, and gain access to new trait trees. Any time before you take a trait from trait tree from your base case, you can replace one tree with a new one you discover from your travels. You will need to get training which takes 1d4 weeks.
You also may buy one talent from a new tree with experience points. You can only have a limited number of talents gain this way based on your character.
level number of talents
1-5 one 2500 xp
6-10 two 5000 xp
15 three 15000 xp
20+ four 30000 xp
Spending in this way cant bring you below last lvl experience lvl