No it's not possible with the approach taken in the link you provided.
That solution uses Xml files that extend the Log4Net framework used by client-managed Qlik Sense. While this works it will give you very basic alert emails.
Much more comprehensive solutions are possible, but require some kind of separate monitoring agent to collect information about the failed reload and then send this as alert emails/Slack/Teams/...
Now, I am obviously biased as I've created such a solution..
It's been around for many years now and proven to be stable and good. It's open source (free!) and runs on almost any hardware, including as a Windows service on the Qlik Sense server itself.
The tool does exactly what you ask for (customising the email subject as well as including log file) and much more. For example, it's possible to control per reload task what user should get alert emails - and if alert emails should be sent at all for that specific task.
