As mentioned in that other thread, modifying /etc/resolv.conf is not a portable solution and so should not be done IMO - so -1 from me for write access via system-files for that.
However there are other VPN snaps in the snap store (e.g. https://snapcraft.io/easy-openvpn-server) which uses firewall-control and network-control so I suspect it is possible to snap a VPN - perhaps @galgalesh may be kind enough to offer some suggestions in your case.