For traits, bring back Mutate Perk as a support perk.
This could part of a research quest related to:
1. The ex-Enclave doctor in NCR who wanted the player in FO2 to test a mutant cure. (It was fatal in FO2)
2. The Brain Rat's idea to use Vault City technology to cure the ghouls in Gecko.
3. Research by the Enclave doctor in Navarro. ( He tested FEV on Deathclaws in FO2 iirc)
4. Perhaps Doctor Fung.
5. Brotherhood of Steel- remember Vree's research from FO1? And the upgrades they could do in FO1 and at the SF base in FO2? They would have at least a military interest in manipulating mutation (probably as an anti-mutant weapon).
Data from the Glow and/or Mariposa may be required to complete the quest.
Maybe even combine data/blueprints from the 5 possible scenarios listed above.
Once available, the procedure would allow removal of traits, swapping of traits, or even extra (3+) traits.
Adding extra traits would be sort of like implants, but each with a disadvantage just like regular traits.
There could be multiple paths available for making this available instead of just one.