If you install this plugin on Spigot then you have access to the following WorldGuard flags:
resourcepack-on-entry
resourcepack-on-exit
String flags with the name of a configured pack as the value and will apply the pack as soon as the region is entered.
entry-without-resourcepack
exit-without-resourcepack
Boolean (allow/deny) flags. Default value is allow. You can bypass it with the same bypass permission as the normal entry and deny flags. If the entry-deny-message or exit-deny-message is set it will send it to the user.
Please note that the flags require at least WorldGuard 6.1.3!