What is the ruling on placing stickers instead of writing by hand on books endowed as an ongoing charity, and is it permissible to remove them?

Your question has two scenarios: The first is that you are an agent for the owner of the books in distributing them, on the condition that "Waqf for Allah" is written on them. The second is that you have bought the books to dedicate them as a waqf, and the merchant stipulated that you write "Waqf for Allah" on them, and this condition is permissible. The condition is fulfilled by writing by hand or by placing stickers with "Waqf for Allah" written on them, as common practice does not differentiate between them. Even if it were assumed that the endower specified writing by hand, it is not obligatory to adhere to that if placing a sticker achieves the purpose and does not defeat the endower's intent, especially given the difficulty of writing by hand. If some people remove the stickers, there is no blame on you.