Is it possible to use the LE client to issue the cert manually and configure your server manually, but still use the cron job for automated certificate renewal?
It’s not because you do not want to run the client completely automatically, but that it would e.g. break a non-supported platform. Additionally you would also have to manually renewal the certs, which can be annoying to do every 90 days.
AFAIK the automatic renewal just uses symbolic link and renames some files, so this may be possible even if the configuration is not possible.
However of course the validation will have to be done before. However I assume most of the validation methods should still work with most platforms.
And if the validation can be done automatically, of course another question is: Can the LE client automatically fetch and validate the certificates, but do not (try to) configure the server?
This way the only you would have to do is to configure your server so that it’s supported on the platform. And if the renewal works too, you would only have to do that once. This would basically be semi-automated.