Dull is difficult to remove, but it can in theory be removed by events that move you towards Shrewd. The most obvious way to do this is to reach rank 4 in the hermetics, then "choose hermetic art", follow the scholar path, and hope for the RNG to smile on you.
I think uncouth is impossible to deliberately remove via normal gameplay. (There might be some random events that move you towards groomed, but I don't think they are at all easy to deliberately trigger.)
FWIW:
- In general, vices (anything with a red background) can be removed eventually via the theology focus.
- I'm pretty sure stubborn is the most difficult-to-remove bad trait, because it doesn't have an opposite. (If you want to "lose X trait" then, in most cases, you should try to trigger an event that "grants opposite-to-X trait". If there is no opposite then this strategy doesn't work, and all you can do is to get your trait count above 6 and hope that the rare event that removes a trait removes stubborn. But I've never had this rare event trigger to remove stubborn, so I don't know if it's even possible.)