File /etc/lighttpd/conf.d/ssl-enable.conf is not configuration file editable by user. It is replaced on every update of package lighttpd-https-cert. So you shouldn’t be editing that file. I would suggest you to unistall said package (it’s part of base system so see: https://www.turris.cz/doc/en/howto/updater#i_deleted_a_package_but_it_came_back), configured your own ssl certificate and then you can use what ever port you want.
Also you can check if you are not editing some file that is part of package and will be replaced with update using pkg_check. It reports some files that are edited as part of standard router operation, such as /etc/root.keys or /etc/config/luci. So just check if it contains files you have edited.