Exposure to radiation should give you good genes too

[Slacker Magician]

As long as its given a ratio similar to how glowing slurry works with majority bad minimal good, it'd limit abuse and I think it'd be "okay" while still allowing some interesting-ish gameplay interactions.

Still slightly abusable via microdosing and adding/removing mutations one at a time, or utilizing a gene scanner to just remove the bad genes entirely while keeping the good ones.