Can they? Absolutely. My dh was the most shy child ever...he used to sit in his grannie's car in 10 degree weather , for hours, rather than go into a home of someone he did not know well. He had to be dragged in, screaming the whole way, that was how much he avoided socializing with anyone but his parents and grannie (who raised him).
This same man, today, uses excellent interpersonal skills to sell Snap-On tools for a living, as a government accounts manager with numerous accounts all over Washington State. To say he learned interpersonal skills in his 20 years in the US Air Force would be understating it. His skills are brilliant now. I admire him as you can tell.
Anyhow, the answer is "yes", such skills can be learned.