Legal Question in Business Law in California

No. Any opinions formed after deposition may be excluded at trial.

Usually one of the deposition questions is, "have you provided me with all of your opinions to which you will testify at trial?" The expert might also be asked if he/she expects to review any other materials before trial. This closes the door on bringing up new stuff at trial. One radical thing one might try to do is withdraw the expert's designation and see if he/she could be replaced. But that might take some major effort. Also, one might threaten the expert by withholding fees for not being prepared for deposition, which is implicit in the agreement to provide expert opinion. I would be concerned that if the expert's testimony were meandering in a controlled deposition situation where the questions generally are predictable, how would the expert appear to a jury?

You have bad experts.