cd /usr/local/ispconfig/interface/ssl/
mv ispserver.crt ispserver.crt-$(date +"%y%m%d%H%M%S").bak
mv ispserver.key ispserver.key-$(date +"%y%m%d%H%M%S").bak
mv ispserver.pem ispserver.pem-$(date +"%y%m%d%H%M%S").bak
ln -s /var/www/clients/client0/webXXX/ssl/`hostname -f`-le.crt ispserver.crt
ln -s  /var/www/clients/client0/webXXX/ssl/`hostname -f`-le.key ispserver.key
cat ispserver.{key,crt} > ispserver.pem
chmod 600 ispserver.pem

Where XXX web number