Yes it is possible to improve a classic but more often then not you will fail if you try. Over time a classic should be re done in some way to keep it relevant. A classic from the 20s is likely not going to have the same effect unless it is redone a bit.
It is possible to improve upon a classic. Just because a movie or a book is considered a classic does not mean that it is just that. Some people do not like classics or just watch it because it is considered one and not because they actually like it very much.
You do not improve on a classic. You can create new classics but why would you want to change classics. Classics became classics for a reason so stop trying to improve or change them. Classics should be left alone and we should be building new things for the future of society.
No, I do not think that you can improve upon a classic. A classic is a classic for a reason, and trying to improve it will only make it worse. A classic is set in a certain point in time, and is meant to be remembered and embraced and not changed.
No, it is not possible to improve upon a classic, because a classic is always the most interesting. A person can modify a classic, but the true value of the classic will always be with the person who did the original work. Everything else is just derivative. While it has value, the original thought is always the most commendable.