It is too late to amend the complaint "as of right" - without leave of court. However, unless "prejudice" to the opposing party can be shown, leave of court to amend is freely granted, at any stage up to, and including trial. Usually, amendments must be made prior to the final pretrial conference, and in time for discovery of expert opinions, their factual basis, and an opportunity to rebut, to occur.
Short answer - there are months, if not years, during which amendments, if sought, would likely be allowed.