I say, and with God's help: Replacing the endowment is permissible with what is more beneficial to people and achieves their interests. However, in our case, the books are beneficial in themselves. If we are not reading them today for certain reasons, we will read them tomorrow. They are considered useful references for some individuals, and we may need to review a topic in them someday, or someone may wish to read them. It is preferable to leave the old books due to their value and importance, and to bring in other books that also benefit people. And God knows best.