You can make up as many rules as you like and key them into whatever data you have in LEM and then you map the rule to an email template, and you can create as many email templates as you need under the manage groups section (don't ask me why, but that's where email templates live).
FIM isn't going to be reading the contents of your files to see whats in them, just tracking CRUD actions basically. If the log happens to be something that LEM already has a connector designed to parse those files then the connector would be able to read into the file, but there isn't a supported way to do your own custom log files and rolling your own, while technically possible, is a real pain and leaves you in an unsupported configuration that could cause you headaches down the line.
A workaround that I've seen in play is to use a script, or have your application itself if you are the developer, that scans the the log and just inserts the relevant data into something like the windows application event logs that LEM is already connected to. Kind of an indirect way to keep tabs on anything that LEM doesn't support natively.