If I installed KDE packages from FreeBSD ISO and updated ports tree, I'd have to upgrade many ports using portmaster or anything else. But during the rebuild, even KDE packages are subject to be replaced. But rebuilding KDE takes 1~2 days even for powerful desktops. So I want to upgrade KDE only from each release of FreeBSD ISO. How can I prevent portmaster from upgrading KDE when rebuilding the ports and keep the system intact?