Hello michael.speth,
Yes, see documentation here:
https://openvpn.net/vpn-server-resources/managing-settings-for-the-web-services-from-the-command-line/#specify-custom-http-headers
cd /usr/local/openvpn_as/scripts/
./sacli --key "cs.http_headers.1" --value "Content-Security-Policy: blablawhatever" ConfigPut
./sacli start
Good luck,
Johan