Is there a word for a high willingness to change your mind/opinion/definition if proven wrong or shown a more accurate truth?
willing to consider ideas and opinions that are new or different to your own.
"Prepared to stand corrected"
Senator Flynn: I thought that was the case, but if I am wrong I am prepared to stand corrected. (Canada. Parliament. Senate, 1974)
I am prepared to stand corrected if someone provides a concrete example of … (Reasonable Man, WP)
I believe that 4H is the best bid possible, though am prepared to stand corrected. (the-west-australian, 9 Feb 2018)
capable of being changed, changeable, molded, trained, etc.; adaptable
and from vocabulary.com:
A malleable [person or] personality is capable of being changed or trained.
It's easier to learn when you're young and malleable. Some, who fancy themselves moderates, admire the businessman’s malleability. But one-fifth of the public lacks a clear positive or negative feeling about the law, a sign that opinions are still malleable.
Malleable can connote manipulation. My sense of being capable of changing one's mind in the face of new facts or information is a desirable malleability.