update feature (in
wp-admin/update-core.php page), it seems to me that wp just replaces all the resources, and the changes that have been made in the working resources just get erased instead of getting merged.
At least I've been experiencing with
wp-login.php that gets replaced per every update and thus I have to reflect back the change from scratch (it's not easy often because the code in the file changes upon update).
Am I right? If so, are there ways to merge the changes already made with the update?