At first sight there is not a lot in this package:
# opkg files zerotier
Package zerotier (1.10.1-1) is installed on root and has the following files:
/usr/bin/zerotier-idtool
/etc/init.d/zerotier
/usr/bin/zerotier-one
/etc/config/zerotier
/usr/bin/zerotier-cli
But if you check /etc/init.d/zerotier you will see
CONFIG_PATH=/var/lib/zerotier-one
and in there:
# ls -al /var/lib/zerotier-one/
drwxr-xr-x 5 root root 200 Aug 16 17:55 .
drwxr-xr-x 4 root root 100 Aug 15 19:32 ..
-rw------- 1 root root 24 Aug 15 19:32 authtoken.secret
drwx------ 4 root root 80 Aug 15 19:32 controller.d
-rw-r--r-- 1 root root 271 Aug 15 19:32 identity.secret
drwxr-xr-x 2 root root 80 Aug 15 19:32 networks.d
drwxr-xr-x 2 root root 40 Sep 15 18:32 peers.d
-rw-r--r-- 1 root root 570 Aug 16 17:55 planet
-rw-r--r-- 1 root root 4 Aug 15 19:32 zerotier-one.pid
-rw-r--r-- 1 root root 4 Aug 15 19:32 zerotier-one.port
So you can probably do this. I don’t know what the package manager will do with this on a package update.