Okay, this is a very difficult sentence. Seems to be from psychology.
I try to tear it into pieces in the hope that you can get the meaning better.
Fähigkeit = ability
Umstellung = switching over to/adjust to + fähig = being able to => adaptability
wenig = less
fest = strong/firmly + gefahren = driven (past tense) => stuck (literally like a car in the mud) or intransigent here.
Persönlichkeit = personality
Struktur = structure
So:
This ability indicates an adaptable and not very steadfast personality structure.