Is it necessary to "reload" subuid/subgid?

After modifying subuid/subgid files (expanding the range), do I need to restart any services or the server itself for LXC to properly apply new range to new containers?

For pure LXC, you’re all good, it runs newuidmap/newgidmap on container startup which parse those files then. For LXD, the daemon parses the files on startup so it needs a restart.