You can unlock the Green Technician branch by completing the Physics degree if you have Discover University. Degrees are the only way to change career branches through normal gameplay.
You might be able to change branches through cheats. Carl's website has a good list. https://www.carls-sims-4-guide.com/cheats.php
There are probably several mods that would let you change your Sim's career to the other branch. I'm not familiar with any of them but I'd check the Master Controller Command Panel (MCCP) mod first if I was going to use mods.