I determined which ports to bump with:
grep --include='*/*/Makefile' --include='*/*/pkg-plist' -r 'EMACS_LIBDIR_WITH_VER\|EMACS_VERSION_SITE_LISPDIR' /usr/ports
Thanks for this. I used to do this by compiling the list of dependent ports from INDEX file, which is broader than these list of changes, and was theoretically good. Although, your approach is better, and seems more precise. Please go ahead.