A statement about one's own opinion can be materially false, and provably (in the sense the word applies in the legal system) so.
Certainly, an attorney can (and this is true of any witness, not just expert witness) coordinate with a witness on a line of questioning which carefully avoids any questions where perjury would be necessary to avoid damaging the case. That's why we have witnesses subject to examinstion by opposing counsel, as well.
Certainly, an attorney can (and this is true of any witness, not just expert witness) coordinate with a witness on a line of questioning which carefully avoids any questions where perjury would be necessary to avoid damaging the case. That's why we have witnesses subject to examinstion by opposing counsel, as well.